CREATE OR REPLACE MATERIALIZED VIEW

From a529a00af40be611e6bed49fe0341b7435a72930 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 21 May 2024 18:35:47 +0200
Subject: [PATCH v2 1/3] Add CREATE OR REPLACE MATERIALIZED VIEW

---
 .../sgml/ref/create_materialized_view.sgml    |  15 +-
 src/backend/commands/createas.c               | 207 ++++++++++++++----
 src/backend/commands/tablecmds.c              |   8 +-
 src/backend/commands/view.c                   | 106 ++++++---
 src/backend/parser/gram.y                     |  15 ++
 src/bin/psql/tab-complete.c                   |  15 +-
 src/include/commands/view.h                   |   3 +
 src/include/nodes/parsenodes.h                |   2 +-
 src/include/nodes/primnodes.h                 |   1 +
 src/test/regress/expected/matview.out         | 191 ++++++++++++++++
 src/test/regress/sql/matview.sql              | 108 +++++++++
 11 files changed, 582 insertions(+), 89 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 0d2fea2b97..b5a8e3441a 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
+CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ USING <replaceable class="parameter">method</replaceable> ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
@@ -60,6 +60,17 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>OR REPLACE</literal></term>
+    <listitem>
+     <para>
+      Replaces a materialized view if it already exists.
+      Specifying <literal>OR REPLACE</literal> together with
+      <literal>IF NOT EXISTS</literal> is an error.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
@@ -67,7 +78,7 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
       Do not throw an error if a materialized view with the same name already
       exists. A notice is issued in this case.  Note that there is no guarantee
       that the existing materialized view is anything like the one that would
-      have been created.
+      have been created, unless you use <literal>OR REPLACE</literal> instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 2c8a93b6e5..c5d78252a1 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -79,55 +79,151 @@ static void intorel_destroy(DestReceiver *self);
 static ObjectAddress
 create_ctas_internal(List *attrList, IntoClause *into)
 {
-	CreateStmt *create = makeNode(CreateStmt);
-	bool		is_matview;
+	bool		is_matview,
+				replace = false;
 	char		relkind;
-	Datum		toast_options;
-	static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+	Oid			matviewOid = InvalidOid;
 	ObjectAddress intoRelationAddr;
 
 	/* This code supports both CREATE TABLE AS and CREATE MATERIALIZED VIEW */
 	is_matview = (into->viewQuery != NULL);
 	relkind = is_matview ? RELKIND_MATVIEW : RELKIND_RELATION;
 
-	/*
-	 * Create the target relation by faking up a CREATE TABLE parsetree and
-	 * passing it to DefineRelation.
-	 */
-	create->relation = into->rel;
-	create->tableElts = attrList;
-	create->inhRelations = NIL;
-	create->ofTypename = NULL;
-	create->constraints = NIL;
-	create->options = into->options;
-	create->oncommit = into->onCommit;
-	create->tablespacename = into->tableSpaceName;
-	create->if_not_exists = false;
-	create->accessMethod = into->accessMethod;
+	/* Check if an existing materialized view needs to be replaced. */
+	if (is_matview)
+	{
+		LOCKMODE	lockmode;
 
-	/*
-	 * Create the relation.  (This will error out if there's an existing view,
-	 * so we don't need more code to complain if "replace" is false.)
-	 */
-	intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL, NULL);
+		lockmode = into->replace ? AccessExclusiveLock : NoLock;
+		(void) RangeVarGetAndCheckCreationNamespace(into->rel, lockmode,
+													&matviewOid);
+		replace = OidIsValid(matviewOid) && into->replace;
+	}
 
-	/*
-	 * If necessary, create a TOAST table for the target table.  Note that
-	 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
-	 * that the TOAST table will be visible for insertion.
-	 */
-	CommandCounterIncrement();
+	if (is_matview && replace)
+	{
+		Relation	rel;
+		List	   *atcmds = NIL;
+		AlterTableCmd *atcmd;
+		TupleDesc	descriptor;
+
+		rel = relation_open(matviewOid, NoLock);
+
+		if (rel->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					errmsg("\"%s\" is not a materialized view",
+						   RelationGetRelationName(rel)));
+
+		CheckTableNotInUse(rel, "CREATE OR REPLACE MATERIALIZED VIEW");
+
+		descriptor = BuildDescForRelation(attrList);
+		checkViewColumns(descriptor, rel->rd_att, true);
+
+		/* Add new attributes via ALTER TABLE. */
+		if (list_length(attrList) > rel->rd_att->natts)
+		{
+			ListCell   *c;
+			int			skip = rel->rd_att->natts;
+
+			foreach(c, attrList)
+			{
+				if (skip > 0)
+				{
+					skip--;
+					continue;
+				}
+				atcmd = makeNode(AlterTableCmd);
+				atcmd->subtype = AT_AddColumnToView;
+				atcmd->def = (Node *) lfirst(c);
+				atcmds = lappend(atcmds, atcmd);
+			}
+		}
+
+		/* Set access method via ALTER TABLE. */
+		if (into->accessMethod != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetAccessMethod;
+			atcmd->name = into->accessMethod;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set tablespace via ALTER TABLE. */
+		if (into->tableSpaceName != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetTableSpace;
+			atcmd->name = into->tableSpaceName;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set storage parameters via ALTER TABLE. */
+		if (into->options != NIL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_ReplaceRelOptions;
+			atcmd->def = (Node *) into->options;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		if (atcmds != NIL)
+		{
+			AlterTableInternal(matviewOid, atcmds, true);
+			CommandCounterIncrement();
+		}
+
+		relation_close(rel, NoLock);
+
+		ObjectAddressSet(intoRelationAddr, RelationRelationId, matviewOid);
+	}
+	else
+	{
+		CreateStmt *create = makeNode(CreateStmt);
+		Datum		toast_options;
+		static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+
+		/*
+		 * Create the target relation by faking up a CREATE TABLE parsetree
+		 * and passing it to DefineRelation.
+		 */
+		create->relation = into->rel;
+		create->tableElts = attrList;
+		create->inhRelations = NIL;
+		create->ofTypename = NULL;
+		create->constraints = NIL;
+		create->options = into->options;
+		create->oncommit = into->onCommit;
+		create->tablespacename = into->tableSpaceName;
+		create->if_not_exists = false;
+		create->accessMethod = into->accessMethod;
+
+		/*
+		 * Create the relation.  (This will error out if there's an existing
+		 * view, so we don't need more code to complain if "replace" is
+		 * false.)
+		 */
+		intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL,
+										  NULL);
 
-	/* parse and validate reloptions for the toast table */
-	toast_options = transformRelOptions((Datum) 0,
-										create->options,
-										"toast",
-										validnsps,
-										true, false);
+		/*
+		 * If necessary, create a TOAST table for the target table.  Note that
+		 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
+		 * that the TOAST table will be visible for insertion.
+		 */
+		CommandCounterIncrement();
+
+		/* parse and validate reloptions for the toast table */
+		toast_options = transformRelOptions((Datum) 0,
+											create->options,
+											"toast",
+											validnsps,
+											true, false);
 
-	(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
+		(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
 
-	NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+		NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+	}
 
 	/* Create the "view" part of a materialized view. */
 	if (is_matview)
@@ -135,7 +231,7 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* StoreViewQuery scribbles on tree, so make a copy */
 		Query	   *query = (Query *) copyObject(into->viewQuery);
 
-		StoreViewQuery(intoRelationAddr.objectId, query, false);
+		StoreViewQuery(intoRelationAddr.objectId, query, replace);
 		CommandCounterIncrement();
 	}
 
@@ -234,7 +330,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 
 	/* Check if the relation exists or not */
 	if (CreateTableAsRelExists(stmt))
+	{
+		/* An existing materialized view can be replaced. */
+		if (is_matview && into->replace)
+		{
+			RefreshMatViewStmt *refresh;
+
+			/* Change the relation to match the new query and other options. */
+			(void) create_ctas_nodata(query->targetList, into);
+
+			/* Refresh the materialized view with a fake statement. */
+			refresh = makeNode(RefreshMatViewStmt);
+			refresh->relation = into->rel;
+			refresh->skipData = into->skipData;
+			refresh->concurrent = false;
+
+			return ExecRefreshMatView(refresh, NULL, NULL, NULL);
+		}
+
 		return InvalidObjectAddress;
+	}
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -395,14 +510,15 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 	oldrelid = get_relname_relid(into->rel->relname, nspid);
 	if (OidIsValid(oldrelid))
 	{
-		if (!ctas->if_not_exists)
+		if (!ctas->if_not_exists && !into->replace)
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_TABLE),
 					 errmsg("relation \"%s\" already exists",
 							into->rel->relname)));
 
 		/*
-		 * The relation exists and IF NOT EXISTS has been specified.
+		 * The relation exists and IF NOT EXISTS or OR REPLACE has been
+		 * specified.
 		 *
 		 * If we are in an extension script, insist that the pre-existing
 		 * object be a member of the extension, to avoid security risks.
@@ -410,11 +526,12 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 		ObjectAddressSet(address, RelationRelationId, oldrelid);
 		checkMembershipInCurrentExtension(&address);
 
-		/* OK to skip */
-		ereport(NOTICE,
-				(errcode(ERRCODE_DUPLICATE_TABLE),
-				 errmsg("relation \"%s\" already exists, skipping",
-						into->rel->relname)));
+		if (ctas->if_not_exists)
+			/* OK to skip */
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							into->rel->relname)));
 		return true;
 	}
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 0b2a52463f..5274daaf3a 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4484,7 +4484,7 @@ AlterTableGetLockLevel(List *cmds)
 				 * Subcommands that may be visible to concurrent SELECTs
 				 */
 			case AT_DropColumn: /* change visible to SELECT */
-			case AT_AddColumnToView:	/* CREATE VIEW */
+			case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			case AT_DropOids:	/* used to equiv to DropColumn */
 			case AT_EnableAlwaysRule:	/* may change SELECT rules */
 			case AT_EnableReplicaRule:	/* may change SELECT rules */
@@ -4795,8 +4795,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
-			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW);
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
+			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW | ATT_MATVIEW);
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, true, cmd,
 							lockmode, context);
 			/* Recursion occurs during execution phase */
@@ -5220,7 +5220,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 	switch (cmd->subtype)
 	{
 		case AT_AddColumn:		/* ADD COLUMN */
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			address = ATExecAddColumn(wqueue, tab, rel, &cmd,
 									  cmd->recurse, false,
 									  lockmode, cur_pass, context);
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index fdad833832..76532aa35d 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -30,8 +30,6 @@
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 
-static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
-
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -130,7 +128,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		 * column list.
 		 */
 		descriptor = BuildDescForRelation(attrList);
-		checkViewColumns(descriptor, rel->rd_att);
+		checkViewColumns(descriptor, rel->rd_att, false);
 
 		/*
 		 * If new attributes have been added, we must add pg_attribute entries
@@ -263,15 +261,22 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
  * added to generate specific complaints.  Also, we allow the new view to have
  * more columns than the old.
  */
-static void
-checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
+void
+checkViewColumns(TupleDesc newdesc, TupleDesc olddesc, bool is_matview)
 {
 	int			i;
 
 	if (newdesc->natts < olddesc->natts)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot drop columns from view")));
+	{
+		if (is_matview)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot drop columns from materialized view"));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot drop columns from view")));
+	}
 
 	for (i = 0; i < olddesc->natts; i++)
 	{
@@ -280,17 +285,34 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 
 		/* XXX msg not right, but we don't support DROP COL on view anyway */
 		if (newattr->attisdropped != oldattr->attisdropped)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot drop columns from view")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot drop columns from materialized view"));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot drop columns from view")));
+		}
 
 		if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							NameStr(newattr->attname)),
-					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change name of materialized view column \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   NameStr(newattr->attname)),
+						errhint("Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead."));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change name of view column \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								NameStr(newattr->attname)),
+						 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		}
 
 		/*
 		 * We cannot allow type, typmod, or collation to change, since these
@@ -299,26 +321,48 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 		 */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change data type of view column \"%s\" from %s to %s",
-							NameStr(oldattr->attname),
-							format_type_with_typemod(oldattr->atttypid,
-													 oldattr->atttypmod),
-							format_type_with_typemod(newattr->atttypid,
-													 newattr->atttypmod))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change data type of materialized view column \"%s\" from %s to %s",
+							   NameStr(oldattr->attname),
+							   format_type_with_typemod(oldattr->atttypid,
+														oldattr->atttypmod),
+							   format_type_with_typemod(newattr->atttypid,
+														newattr->atttypmod)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change data type of view column \"%s\" from %s to %s",
+								NameStr(oldattr->attname),
+								format_type_with_typemod(oldattr->atttypid,
+														 oldattr->atttypmod),
+								format_type_with_typemod(newattr->atttypid,
+														 newattr->atttypmod))));
+		}
 
 		/*
 		 * At this point, attcollations should be both valid or both invalid,
 		 * so applying get_collation_name unconditionally should be fine.
 		 */
 		if (newattr->attcollation != oldattr->attcollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							get_collation_name(oldattr->attcollation),
-							get_collation_name(newattr->attcollation))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change collation of materialized view column \"%s\" from \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   get_collation_name(oldattr->attcollation),
+							   get_collation_name(newattr->attcollation)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								get_collation_name(oldattr->attcollation),
+								get_collation_name(newattr->attcollation))));
+		}
 	}
 
 	/*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index a043fd4c66..ed477806d1 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4831,6 +4831,21 @@ CreateMatViewStmt:
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = !($10);
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 891face1b6..f3291e79d8 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1811,7 +1811,7 @@ psql_completion(const char *text, int start, int end)
 	/* complete with something you can create or replace */
 	else if (TailMatches("CREATE", "OR", "REPLACE"))
 		COMPLETE_WITH("FUNCTION", "PROCEDURE", "LANGUAGE", "RULE", "VIEW",
-					  "AGGREGATE", "TRANSFORM", "TRIGGER");
+					  "AGGREGATE", "TRANSFORM", "TRIGGER", "MATERIALIZED VIEW");
 
 /* DROP, but not DROP embedded in other commands */
 	/* complete with something you can drop */
@@ -3619,13 +3619,16 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("SELECT");
 
 /* CREATE MATERIALIZED VIEW */
-	else if (Matches("CREATE", "MATERIALIZED"))
+	else if (Matches("CREATE", "MATERIALIZED") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED"))
 		COMPLETE_WITH("VIEW");
-	/* Complete CREATE MATERIALIZED VIEW <name> with AS */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> with AS */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("AS");
-	/* Complete "CREATE MATERIALIZED VIEW <sth> AS with "SELECT" */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS"))
+	/* Complete "CREATE [ OR REPLACE ] MATERIALIZED VIEW <sth> AS with "SELECT" */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "AS"))
 		COMPLETE_WITH("SELECT");
 
 /* CREATE EVENT TRIGGER */
diff --git a/src/include/commands/view.h b/src/include/commands/view.h
index d2d8588989..7eacdaaceb 100644
--- a/src/include/commands/view.h
+++ b/src/include/commands/view.h
@@ -22,4 +22,7 @@ extern ObjectAddress DefineView(ViewStmt *stmt, const char *queryString,
 
 extern void StoreViewQuery(Oid viewOid, Query *viewParse, bool replace);
 
+extern void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc,
+							 bool is_matview);
+
 #endif							/* VIEW_H */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 85a62b538e..cbc4b608e3 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2351,7 +2351,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
-	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
+	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE [MATERIALIZED] VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_CookedColumnDefault,		/* add a pre-cooked column default */
 	AT_DropNotNull,				/* alter column drop not null */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index ea47652adb..4b0ee5d10d 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	Node	   *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 038ab73517..e2e2a13396 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -694,3 +694,194 @@ NOTICE:  relation "matview_ine_tab" already exists, skipping
 (0 rows)
 
 DROP MATERIALIZED VIEW matview_ine_tab;
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+NOTICE:  materialized view "mvtest_replace" does not exist, skipping
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 1
+(1 row)
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 2
+(1 row)
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+ERROR:  materialized view "mvtest_replace" has not been populated
+HINT:  Use the REFRESH MATERIALIZED VIEW command.
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 4 | 1
+(1 row)
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 4 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     |   reloptions    |     spcname      | amname 
+---+---+----------------+-----------------+------------------+--------
+ 5 | 1 | mvtest_replace | {fillfactor=50} | regress_tblspace | heap2
+(1 row)
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+ a | b | a | b 
+---+---+---+---
+ 6 | 1 | 6 | 1
+(1 row)
+
+DROP VIEW mvtest_replace_v;
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+RESET enable_seqscan;
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+ERROR:  cannot change data type of materialized view column "b" from integer to text
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+ERROR:  cannot change name of materialized view column "b" to "b2"
+HINT:  Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead.
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+ERROR:  cannot change collation of materialized view column "c" from "C" to "POSIX"
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+ERROR:  cannot drop columns from materialized view
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+ERROR:  "mvtest_not_mv" is not a materialized view
+DROP VIEW mvtest_not_mv;
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+ERROR:  syntax error at or near "NOT"
+LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
+                                               ^
+DROP MATERIALIZED VIEW mvtest_replace;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index b74ee305e0..c12f0243c9 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -314,3 +314,111 @@ EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
 DROP MATERIALIZED VIEW matview_ine_tab;
+
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+DROP VIEW mvtest_replace_v;
+
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+SELECT * FROM mvtest_replace;
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+DROP VIEW mvtest_not_mv;
+
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+
+DROP MATERIALIZED VIEW mvtest_replace;
-- 
2.45.2

From f0ed9b74e50530abefb2edc51603c8df061eaa22 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 28 May 2024 02:19:53 +0200
Subject: [PATCH v2 2/3] Deprecate CREATE MATERIALIZED VIEW IF NOT EXISTS

---
 src/backend/parser/gram.y                     | 14 +++++++++++++
 .../expected/test_extensions.out              | 18 +++++++++++++++++
 src/test/regress/expected/matview.out         | 20 +++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index ed477806d1..b1100bdec1 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4830,6 +4830,20 @@ CreateMatViewStmt:
 					$8->rel->relpersistence = $2;
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
+
+					if (ctas->into->rel->schemaname)
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.%s.",
+											ctas->into->rel->schemaname,
+											ctas->into->rel->relname),
+									parser_errposition(@1));
+					else
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.",
+											ctas->into->rel->relname),
+									parser_errposition(@1));
 				}
 		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
 				{
diff --git a/src/test/modules/test_extensions/expected/test_extensions.out b/src/test/modules/test_extensions/expected/test_extensions.out
index f357cc21aa..ecd453b29d 100644
--- a/src/test/modules/test_extensions/expected/test_extensions.out
+++ b/src/test/modules/test_extensions/expected/test_extensions.out
@@ -377,41 +377,57 @@ Objects in extension "test_ext_cor"
 CREATE COLLATION ext_cine_coll
   ( LC_COLLATE = "C", LC_CTYPE = "C" );
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  collation ext_cine_coll is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP COLLATION ext_cine_coll;
 CREATE MATERIALIZED VIEW ext_cine_mv AS SELECT 11 AS f1;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  materialized view ext_cine_mv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP MATERIALIZED VIEW ext_cine_mv;
 CREATE FOREIGN DATA WRAPPER dummy;
 CREATE SERVER ext_cine_srv FOREIGN DATA WRAPPER dummy;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  server ext_cine_srv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP SERVER ext_cine_srv;
 CREATE SCHEMA ext_cine_schema;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  schema ext_cine_schema is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP SCHEMA ext_cine_schema;
 CREATE SEQUENCE ext_cine_seq;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  sequence ext_cine_seq is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP SEQUENCE ext_cine_seq;
 CREATE TABLE ext_cine_tab1 (x int);
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  table ext_cine_tab1 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP TABLE ext_cine_tab1;
 CREATE TABLE ext_cine_tab2 AS SELECT 42 AS y;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  table ext_cine_tab2 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP TABLE ext_cine_tab2;
 CREATE EXTENSION test_ext_cine;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
@@ -433,6 +449,8 @@ Objects in extension "test_ext_cine"
 (14 rows)
 
 ALTER EXTENSION test_ext_cine UPDATE TO '1.1';
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index e2e2a13396..cefd0d442c 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -565,6 +565,10 @@ CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 ERROR:  relation "mvtest_mv_foo" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELE...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW mvtest_mv_foo.
 NOTICE:  relation "mvtest_mv_foo" already exists, skipping
 CREATE UNIQUE INDEX ON mvtest_mv_foo (i);
 RESET ROLE;
@@ -662,12 +666,20 @@ CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 CREATE MATERIALIZED VIEW matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW matview_ine_tab AS
@@ -676,6 +688,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
@@ -688,6 +704,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
-- 
2.45.2

From c386742310dcf2429b796c2a2d32f12db2cc419f Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Fri, 26 Jul 2024 23:33:15 +0200
Subject: [PATCH v2 3/3] Replace matview WITH OLD DATA

---
 .../sgml/ref/create_materialized_view.sgml    | 16 +++++++++--
 src/backend/commands/createas.c               | 26 +++++++++++------
 src/backend/parser/gram.y                     | 16 +++++++++++
 src/include/nodes/primnodes.h                 |  1 +
 src/test/regress/expected/matview.out         | 28 +++++++++++++++++++
 src/test/regress/sql/matview.sql              | 15 ++++++++++
 6 files changed, 90 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index b5a8e3441a..65633b8bfa 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -27,7 +27,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     AS <replaceable>query</replaceable>
-    [ WITH [ NO ] DATA ]
+    [ WITH [ NO | OLD ] DATA ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -37,7 +37,8 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
   <para>
    <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
    a query.  The query is executed and used to populate the view at the time
-   the command is issued (unless <command>WITH NO DATA</command> is used) and may be
+   the command is issued (unless <command>WITH NO DATA</command> or
+   <command>WITH OLD DATA</command> is used) and may be
    refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
   </para>
 
@@ -160,7 +161,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
    </varlistentry>
 
    <varlistentry>
-    <term><literal>WITH [ NO ] DATA</literal></term>
+    <term><literal>WITH [ NO | OLD ] DATA</literal></term>
     <listitem>
      <para>
       This clause specifies whether or not the materialized view should be
@@ -168,6 +169,15 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
       flagged as unscannable and cannot be queried until <command>REFRESH
       MATERIALIZED VIEW</command> is used.
      </para>
+
+     <para>
+      The form <command>WITH OLD DATA</command> keeps the already stored data
+      when replacing an existing materialized view to keep it populated.  For
+      newly created materialized views, this has the same effect as
+      <command>WITH DATA</command>.  Use this form if you want to use
+      <command>REFRESH MATERIALIZED VIEW CONCURRENTLY</command> as it requires
+      a populated materialized view.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index c5d78252a1..e2948ac966 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -334,18 +334,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* An existing materialized view can be replaced. */
 		if (is_matview && into->replace)
 		{
-			RefreshMatViewStmt *refresh;
-
 			/* Change the relation to match the new query and other options. */
-			(void) create_ctas_nodata(query->targetList, into);
+			address = create_ctas_nodata(query->targetList, into);
 
-			/* Refresh the materialized view with a fake statement. */
-			refresh = makeNode(RefreshMatViewStmt);
-			refresh->relation = into->rel;
-			refresh->skipData = into->skipData;
-			refresh->concurrent = false;
+			/*
+			 * Refresh the materialized view with a fake statement unless we
+			 * must keep the old data.
+			 */
+			if (!into->keepData)
+			{
+				RefreshMatViewStmt *refresh;
+
+				refresh = makeNode(RefreshMatViewStmt);
+				refresh->relation = into->rel;
+				refresh->skipData = into->skipData;
+				refresh->concurrent = false;
+
+				address = ExecRefreshMatView(refresh, NULL, NULL, NULL);
+			}
 
-			return ExecRefreshMatView(refresh, NULL, NULL, NULL);
+			return address;
 		}
 
 		return InvalidObjectAddress;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index b1100bdec1..0647955005 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4860,6 +4860,22 @@ CreateMatViewStmt:
 					$7->replace = true;
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt WITH OLD DATA_P
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = false;
+					$7->keepData = true;
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 4b0ee5d10d..ae84cb522e 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	Node	   *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		keepData;		/* true for WITH OLD DATA */
 	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index cefd0d442c..47dfd88bff 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -751,6 +751,23 @@ SELECT * FROM mvtest_replace;
  3
 (1 row)
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 5
+(1 row)
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -905,3 +922,14 @@ ERROR:  syntax error at or near "NOT"
 LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
                                                ^
 DROP MATERIALIZED VIEW mvtest_replace;
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a  
+----
+ 17
+(1 row)
+
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index c12f0243c9..b268237c24 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -338,6 +338,14 @@ SELECT * FROM mvtest_replace; -- error: not populated
 REFRESH MATERIALIZED VIEW mvtest_replace;
 SELECT * FROM mvtest_replace;
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -422,3 +430,10 @@ CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
   SELECT 1 AS a;
 
 DROP MATERIALIZED VIEW mvtest_replace;
+
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
-- 
2.45.2

From 158f025fa2696a4a807def4a3c533982cfd7b318 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 21 May 2024 18:35:47 +0200
Subject: [PATCH v3 1/3] Add CREATE OR REPLACE MATERIALIZED VIEW

---
 .../sgml/ref/create_materialized_view.sgml    |  15 +-
 src/backend/commands/createas.c               | 207 ++++++++++++++----
 src/backend/commands/tablecmds.c              |   8 +-
 src/backend/commands/view.c                   | 106 ++++++---
 src/backend/parser/gram.y                     |  15 ++
 src/bin/psql/tab-complete.c                   |  15 +-
 src/include/commands/view.h                   |   3 +
 src/include/nodes/parsenodes.h                |   2 +-
 src/include/nodes/primnodes.h                 |   1 +
 src/test/regress/expected/matview.out         | 191 ++++++++++++++++
 src/test/regress/sql/matview.sql              | 108 +++++++++
 11 files changed, 582 insertions(+), 89 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 0d2fea2b97..b5a8e3441a 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
+CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ USING <replaceable class="parameter">method</replaceable> ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
@@ -60,6 +60,17 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>OR REPLACE</literal></term>
+    <listitem>
+     <para>
+      Replaces a materialized view if it already exists.
+      Specifying <literal>OR REPLACE</literal> together with
+      <literal>IF NOT EXISTS</literal> is an error.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
@@ -67,7 +78,7 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
       Do not throw an error if a materialized view with the same name already
       exists. A notice is issued in this case.  Note that there is no guarantee
       that the existing materialized view is anything like the one that would
-      have been created.
+      have been created, unless you use <literal>OR REPLACE</literal> instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 0b629b1f79..e4ed3748f9 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -79,55 +79,151 @@ static void intorel_destroy(DestReceiver *self);
 static ObjectAddress
 create_ctas_internal(List *attrList, IntoClause *into)
 {
-	CreateStmt *create = makeNode(CreateStmt);
-	bool		is_matview;
+	bool		is_matview,
+				replace = false;
 	char		relkind;
-	Datum		toast_options;
-	const char *const validnsps[] = HEAP_RELOPT_NAMESPACES;
+	Oid			matviewOid = InvalidOid;
 	ObjectAddress intoRelationAddr;
 
 	/* This code supports both CREATE TABLE AS and CREATE MATERIALIZED VIEW */
 	is_matview = (into->viewQuery != NULL);
 	relkind = is_matview ? RELKIND_MATVIEW : RELKIND_RELATION;
 
-	/*
-	 * Create the target relation by faking up a CREATE TABLE parsetree and
-	 * passing it to DefineRelation.
-	 */
-	create->relation = into->rel;
-	create->tableElts = attrList;
-	create->inhRelations = NIL;
-	create->ofTypename = NULL;
-	create->constraints = NIL;
-	create->options = into->options;
-	create->oncommit = into->onCommit;
-	create->tablespacename = into->tableSpaceName;
-	create->if_not_exists = false;
-	create->accessMethod = into->accessMethod;
+	/* Check if an existing materialized view needs to be replaced. */
+	if (is_matview)
+	{
+		LOCKMODE	lockmode;
 
-	/*
-	 * Create the relation.  (This will error out if there's an existing view,
-	 * so we don't need more code to complain if "replace" is false.)
-	 */
-	intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL, NULL);
+		lockmode = into->replace ? AccessExclusiveLock : NoLock;
+		(void) RangeVarGetAndCheckCreationNamespace(into->rel, lockmode,
+													&matviewOid);
+		replace = OidIsValid(matviewOid) && into->replace;
+	}
 
-	/*
-	 * If necessary, create a TOAST table for the target table.  Note that
-	 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
-	 * that the TOAST table will be visible for insertion.
-	 */
-	CommandCounterIncrement();
+	if (is_matview && replace)
+	{
+		Relation	rel;
+		List	   *atcmds = NIL;
+		AlterTableCmd *atcmd;
+		TupleDesc	descriptor;
+
+		rel = relation_open(matviewOid, NoLock);
+
+		if (rel->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					errmsg("\"%s\" is not a materialized view",
+						   RelationGetRelationName(rel)));
+
+		CheckTableNotInUse(rel, "CREATE OR REPLACE MATERIALIZED VIEW");
+
+		descriptor = BuildDescForRelation(attrList);
+		checkViewColumns(descriptor, rel->rd_att, true);
+
+		/* Add new attributes via ALTER TABLE. */
+		if (list_length(attrList) > rel->rd_att->natts)
+		{
+			ListCell   *c;
+			int			skip = rel->rd_att->natts;
+
+			foreach(c, attrList)
+			{
+				if (skip > 0)
+				{
+					skip--;
+					continue;
+				}
+				atcmd = makeNode(AlterTableCmd);
+				atcmd->subtype = AT_AddColumnToView;
+				atcmd->def = (Node *) lfirst(c);
+				atcmds = lappend(atcmds, atcmd);
+			}
+		}
+
+		/* Set access method via ALTER TABLE. */
+		if (into->accessMethod != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetAccessMethod;
+			atcmd->name = into->accessMethod;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set tablespace via ALTER TABLE. */
+		if (into->tableSpaceName != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetTableSpace;
+			atcmd->name = into->tableSpaceName;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set storage parameters via ALTER TABLE. */
+		if (into->options != NIL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_ReplaceRelOptions;
+			atcmd->def = (Node *) into->options;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		if (atcmds != NIL)
+		{
+			AlterTableInternal(matviewOid, atcmds, true);
+			CommandCounterIncrement();
+		}
+
+		relation_close(rel, NoLock);
+
+		ObjectAddressSet(intoRelationAddr, RelationRelationId, matviewOid);
+	}
+	else
+	{
+		CreateStmt *create = makeNode(CreateStmt);
+		Datum		toast_options;
+		const static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+
+		/*
+		 * Create the target relation by faking up a CREATE TABLE parsetree
+		 * and passing it to DefineRelation.
+		 */
+		create->relation = into->rel;
+		create->tableElts = attrList;
+		create->inhRelations = NIL;
+		create->ofTypename = NULL;
+		create->constraints = NIL;
+		create->options = into->options;
+		create->oncommit = into->onCommit;
+		create->tablespacename = into->tableSpaceName;
+		create->if_not_exists = false;
+		create->accessMethod = into->accessMethod;
+
+		/*
+		 * Create the relation.  (This will error out if there's an existing
+		 * view, so we don't need more code to complain if "replace" is
+		 * false.)
+		 */
+		intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL,
+										  NULL);
 
-	/* parse and validate reloptions for the toast table */
-	toast_options = transformRelOptions((Datum) 0,
-										create->options,
-										"toast",
-										validnsps,
-										true, false);
+		/*
+		 * If necessary, create a TOAST table for the target table.  Note that
+		 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
+		 * that the TOAST table will be visible for insertion.
+		 */
+		CommandCounterIncrement();
+
+		/* parse and validate reloptions for the toast table */
+		toast_options = transformRelOptions((Datum) 0,
+											create->options,
+											"toast",
+											validnsps,
+											true, false);
 
-	(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
+		(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
 
-	NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+		NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+	}
 
 	/* Create the "view" part of a materialized view. */
 	if (is_matview)
@@ -135,7 +231,7 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* StoreViewQuery scribbles on tree, so make a copy */
 		Query	   *query = (Query *) copyObject(into->viewQuery);
 
-		StoreViewQuery(intoRelationAddr.objectId, query, false);
+		StoreViewQuery(intoRelationAddr.objectId, query, replace);
 		CommandCounterIncrement();
 	}
 
@@ -231,7 +327,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 
 	/* Check if the relation exists or not */
 	if (CreateTableAsRelExists(stmt))
+	{
+		/* An existing materialized view can be replaced. */
+		if (is_matview && into->replace)
+		{
+			RefreshMatViewStmt *refresh;
+
+			/* Change the relation to match the new query and other options. */
+			(void) create_ctas_nodata(query->targetList, into);
+
+			/* Refresh the materialized view with a fake statement. */
+			refresh = makeNode(RefreshMatViewStmt);
+			refresh->relation = into->rel;
+			refresh->skipData = into->skipData;
+			refresh->concurrent = false;
+
+			return ExecRefreshMatView(refresh, NULL, NULL);
+		}
+
 		return InvalidObjectAddress;
+	}
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -392,14 +507,15 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 	oldrelid = get_relname_relid(into->rel->relname, nspid);
 	if (OidIsValid(oldrelid))
 	{
-		if (!ctas->if_not_exists)
+		if (!ctas->if_not_exists && !into->replace)
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_TABLE),
 					 errmsg("relation \"%s\" already exists",
 							into->rel->relname)));
 
 		/*
-		 * The relation exists and IF NOT EXISTS has been specified.
+		 * The relation exists and IF NOT EXISTS or OR REPLACE has been
+		 * specified.
 		 *
 		 * If we are in an extension script, insist that the pre-existing
 		 * object be a member of the extension, to avoid security risks.
@@ -407,11 +523,12 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 		ObjectAddressSet(address, RelationRelationId, oldrelid);
 		checkMembershipInCurrentExtension(&address);
 
-		/* OK to skip */
-		ereport(NOTICE,
-				(errcode(ERRCODE_DUPLICATE_TABLE),
-				 errmsg("relation \"%s\" already exists, skipping",
-						into->rel->relname)));
+		if (ctas->if_not_exists)
+			/* OK to skip */
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							into->rel->relname)));
 		return true;
 	}
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index b3cc6f8f69..bcc08f9420 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4480,7 +4480,7 @@ AlterTableGetLockLevel(List *cmds)
 				 * Subcommands that may be visible to concurrent SELECTs
 				 */
 			case AT_DropColumn: /* change visible to SELECT */
-			case AT_AddColumnToView:	/* CREATE VIEW */
+			case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			case AT_DropOids:	/* used to equiv to DropColumn */
 			case AT_EnableAlwaysRule:	/* may change SELECT rules */
 			case AT_EnableReplicaRule:	/* may change SELECT rules */
@@ -4783,8 +4783,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
-			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW);
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
+			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW | ATT_MATVIEW);
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, true, cmd,
 							lockmode, context);
 			/* Recursion occurs during execution phase */
@@ -5178,7 +5178,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 	switch (cmd->subtype)
 	{
 		case AT_AddColumn:		/* ADD COLUMN */
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			address = ATExecAddColumn(wqueue, tab, rel, &cmd,
 									  cmd->recurse, false,
 									  lockmode, cur_pass, context);
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index fdad833832..76532aa35d 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -30,8 +30,6 @@
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 
-static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
-
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -130,7 +128,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		 * column list.
 		 */
 		descriptor = BuildDescForRelation(attrList);
-		checkViewColumns(descriptor, rel->rd_att);
+		checkViewColumns(descriptor, rel->rd_att, false);
 
 		/*
 		 * If new attributes have been added, we must add pg_attribute entries
@@ -263,15 +261,22 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
  * added to generate specific complaints.  Also, we allow the new view to have
  * more columns than the old.
  */
-static void
-checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
+void
+checkViewColumns(TupleDesc newdesc, TupleDesc olddesc, bool is_matview)
 {
 	int			i;
 
 	if (newdesc->natts < olddesc->natts)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot drop columns from view")));
+	{
+		if (is_matview)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot drop columns from materialized view"));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot drop columns from view")));
+	}
 
 	for (i = 0; i < olddesc->natts; i++)
 	{
@@ -280,17 +285,34 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 
 		/* XXX msg not right, but we don't support DROP COL on view anyway */
 		if (newattr->attisdropped != oldattr->attisdropped)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot drop columns from view")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot drop columns from materialized view"));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot drop columns from view")));
+		}
 
 		if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							NameStr(newattr->attname)),
-					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change name of materialized view column \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   NameStr(newattr->attname)),
+						errhint("Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead."));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change name of view column \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								NameStr(newattr->attname)),
+						 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		}
 
 		/*
 		 * We cannot allow type, typmod, or collation to change, since these
@@ -299,26 +321,48 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 		 */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change data type of view column \"%s\" from %s to %s",
-							NameStr(oldattr->attname),
-							format_type_with_typemod(oldattr->atttypid,
-													 oldattr->atttypmod),
-							format_type_with_typemod(newattr->atttypid,
-													 newattr->atttypmod))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change data type of materialized view column \"%s\" from %s to %s",
+							   NameStr(oldattr->attname),
+							   format_type_with_typemod(oldattr->atttypid,
+														oldattr->atttypmod),
+							   format_type_with_typemod(newattr->atttypid,
+														newattr->atttypmod)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change data type of view column \"%s\" from %s to %s",
+								NameStr(oldattr->attname),
+								format_type_with_typemod(oldattr->atttypid,
+														 oldattr->atttypmod),
+								format_type_with_typemod(newattr->atttypid,
+														 newattr->atttypmod))));
+		}
 
 		/*
 		 * At this point, attcollations should be both valid or both invalid,
 		 * so applying get_collation_name unconditionally should be fine.
 		 */
 		if (newattr->attcollation != oldattr->attcollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							get_collation_name(oldattr->attcollation),
-							get_collation_name(newattr->attcollation))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change collation of materialized view column \"%s\" from \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   get_collation_name(oldattr->attcollation),
+							   get_collation_name(newattr->attcollation)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								get_collation_name(oldattr->attcollation),
+								get_collation_name(newattr->attcollation))));
+		}
 	}
 
 	/*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 84cef57a70..b02b2f42d2 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4779,6 +4779,21 @@ CreateMatViewStmt:
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = !($10);
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index a7ccde6d7d..c50a3781db 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1811,7 +1811,7 @@ psql_completion(const char *text, int start, int end)
 	/* complete with something you can create or replace */
 	else if (TailMatches("CREATE", "OR", "REPLACE"))
 		COMPLETE_WITH("FUNCTION", "PROCEDURE", "LANGUAGE", "RULE", "VIEW",
-					  "AGGREGATE", "TRANSFORM", "TRIGGER");
+					  "AGGREGATE", "TRANSFORM", "TRIGGER", "MATERIALIZED VIEW");
 
 /* DROP, but not DROP embedded in other commands */
 	/* complete with something you can drop */
@@ -3599,13 +3599,16 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("SELECT");
 
 /* CREATE MATERIALIZED VIEW */
-	else if (Matches("CREATE", "MATERIALIZED"))
+	else if (Matches("CREATE", "MATERIALIZED") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED"))
 		COMPLETE_WITH("VIEW");
-	/* Complete CREATE MATERIALIZED VIEW <name> with AS */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> with AS */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("AS");
-	/* Complete "CREATE MATERIALIZED VIEW <sth> AS with "SELECT" */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS"))
+	/* Complete "CREATE [ OR REPLACE ] MATERIALIZED VIEW <sth> AS with "SELECT" */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "AS"))
 		COMPLETE_WITH("SELECT");
 
 /* CREATE EVENT TRIGGER */
diff --git a/src/include/commands/view.h b/src/include/commands/view.h
index d2d8588989..7eacdaaceb 100644
--- a/src/include/commands/view.h
+++ b/src/include/commands/view.h
@@ -22,4 +22,7 @@ extern ObjectAddress DefineView(ViewStmt *stmt, const char *queryString,
 
 extern void StoreViewQuery(Oid viewOid, Query *viewParse, bool replace);
 
+extern void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc,
+							 bool is_matview);
+
 #endif							/* VIEW_H */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 124d853e49..3ba536eee3 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2338,7 +2338,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
-	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
+	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE [MATERIALIZED] VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_CookedColumnDefault,		/* add a pre-cooked column default */
 	AT_DropNotNull,				/* alter column drop not null */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index ea47652adb..4b0ee5d10d 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	Node	   *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 038ab73517..e2e2a13396 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -694,3 +694,194 @@ NOTICE:  relation "matview_ine_tab" already exists, skipping
 (0 rows)
 
 DROP MATERIALIZED VIEW matview_ine_tab;
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+NOTICE:  materialized view "mvtest_replace" does not exist, skipping
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 1
+(1 row)
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 2
+(1 row)
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+ERROR:  materialized view "mvtest_replace" has not been populated
+HINT:  Use the REFRESH MATERIALIZED VIEW command.
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 4 | 1
+(1 row)
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 4 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     |   reloptions    |     spcname      | amname 
+---+---+----------------+-----------------+------------------+--------
+ 5 | 1 | mvtest_replace | {fillfactor=50} | regress_tblspace | heap2
+(1 row)
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+ a | b | a | b 
+---+---+---+---
+ 6 | 1 | 6 | 1
+(1 row)
+
+DROP VIEW mvtest_replace_v;
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+RESET enable_seqscan;
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+ERROR:  cannot change data type of materialized view column "b" from integer to text
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+ERROR:  cannot change name of materialized view column "b" to "b2"
+HINT:  Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead.
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+ERROR:  cannot change collation of materialized view column "c" from "C" to "POSIX"
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+ERROR:  cannot drop columns from materialized view
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+ERROR:  "mvtest_not_mv" is not a materialized view
+DROP VIEW mvtest_not_mv;
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+ERROR:  syntax error at or near "NOT"
+LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
+                                               ^
+DROP MATERIALIZED VIEW mvtest_replace;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index b74ee305e0..c12f0243c9 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -314,3 +314,111 @@ EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
 DROP MATERIALIZED VIEW matview_ine_tab;
+
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+DROP VIEW mvtest_replace_v;
+
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+SELECT * FROM mvtest_replace;
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+DROP VIEW mvtest_not_mv;
+
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+
+DROP MATERIALIZED VIEW mvtest_replace;
-- 
2.46.0

From 28c5700bae846c2ce3cb0ca552f5dca256420a9e Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 28 May 2024 02:19:53 +0200
Subject: [PATCH v3 2/3] Deprecate CREATE MATERIALIZED VIEW IF NOT EXISTS

---
 src/backend/parser/gram.y                     | 14 +++++++++++++
 .../expected/test_extensions.out              | 18 +++++++++++++++++
 src/test/regress/expected/matview.out         | 20 +++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index b02b2f42d2..4b939ea7ca 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4778,6 +4778,20 @@ CreateMatViewStmt:
 					$8->rel->relpersistence = $2;
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
+
+					if (ctas->into->rel->schemaname)
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.%s.",
+											ctas->into->rel->schemaname,
+											ctas->into->rel->relname),
+									parser_errposition(@1));
+					else
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.",
+											ctas->into->rel->relname),
+									parser_errposition(@1));
 				}
 		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
 				{
diff --git a/src/test/modules/test_extensions/expected/test_extensions.out b/src/test/modules/test_extensions/expected/test_extensions.out
index f357cc21aa..ecd453b29d 100644
--- a/src/test/modules/test_extensions/expected/test_extensions.out
+++ b/src/test/modules/test_extensions/expected/test_extensions.out
@@ -377,41 +377,57 @@ Objects in extension "test_ext_cor"
 CREATE COLLATION ext_cine_coll
   ( LC_COLLATE = "C", LC_CTYPE = "C" );
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  collation ext_cine_coll is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP COLLATION ext_cine_coll;
 CREATE MATERIALIZED VIEW ext_cine_mv AS SELECT 11 AS f1;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  materialized view ext_cine_mv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP MATERIALIZED VIEW ext_cine_mv;
 CREATE FOREIGN DATA WRAPPER dummy;
 CREATE SERVER ext_cine_srv FOREIGN DATA WRAPPER dummy;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  server ext_cine_srv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP SERVER ext_cine_srv;
 CREATE SCHEMA ext_cine_schema;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  schema ext_cine_schema is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP SCHEMA ext_cine_schema;
 CREATE SEQUENCE ext_cine_seq;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  sequence ext_cine_seq is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP SEQUENCE ext_cine_seq;
 CREATE TABLE ext_cine_tab1 (x int);
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  table ext_cine_tab1 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP TABLE ext_cine_tab1;
 CREATE TABLE ext_cine_tab2 AS SELECT 42 AS y;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 ERROR:  table ext_cine_tab2 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 DROP TABLE ext_cine_tab2;
 CREATE EXTENSION test_ext_cine;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
@@ -433,6 +449,8 @@ Objects in extension "test_ext_cine"
 (14 rows)
 
 ALTER EXTENSION test_ext_cine UPDATE TO '1.1';
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index e2e2a13396..cefd0d442c 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -565,6 +565,10 @@ CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 ERROR:  relation "mvtest_mv_foo" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELE...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW mvtest_mv_foo.
 NOTICE:  relation "mvtest_mv_foo" already exists, skipping
 CREATE UNIQUE INDEX ON mvtest_mv_foo (i);
 RESET ROLE;
@@ -662,12 +666,20 @@ CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 CREATE MATERIALIZED VIEW matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW matview_ine_tab AS
@@ -676,6 +688,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
@@ -688,6 +704,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
-- 
2.46.0

From db9be5bcfb8a8f2e63386004a68b7b026d56e9df Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Fri, 26 Jul 2024 23:33:15 +0200
Subject: [PATCH v3 3/3] Replace matview WITH OLD DATA

---
 .../sgml/ref/create_materialized_view.sgml    | 16 +++++++++--
 src/backend/commands/createas.c               | 26 +++++++++++------
 src/backend/parser/gram.y                     | 16 +++++++++++
 src/include/nodes/primnodes.h                 |  1 +
 src/test/regress/expected/matview.out         | 28 +++++++++++++++++++
 src/test/regress/sql/matview.sql              | 15 ++++++++++
 6 files changed, 90 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index b5a8e3441a..65633b8bfa 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -27,7 +27,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     AS <replaceable>query</replaceable>
-    [ WITH [ NO ] DATA ]
+    [ WITH [ NO | OLD ] DATA ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -37,7 +37,8 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
   <para>
    <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
    a query.  The query is executed and used to populate the view at the time
-   the command is issued (unless <command>WITH NO DATA</command> is used) and may be
+   the command is issued (unless <command>WITH NO DATA</command> or
+   <command>WITH OLD DATA</command> is used) and may be
    refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
   </para>
 
@@ -160,7 +161,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
    </varlistentry>
 
    <varlistentry>
-    <term><literal>WITH [ NO ] DATA</literal></term>
+    <term><literal>WITH [ NO | OLD ] DATA</literal></term>
     <listitem>
      <para>
       This clause specifies whether or not the materialized view should be
@@ -168,6 +169,15 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
       flagged as unscannable and cannot be queried until <command>REFRESH
       MATERIALIZED VIEW</command> is used.
      </para>
+
+     <para>
+      The form <command>WITH OLD DATA</command> keeps the already stored data
+      when replacing an existing materialized view to keep it populated.  For
+      newly created materialized views, this has the same effect as
+      <command>WITH DATA</command>.  Use this form if you want to use
+      <command>REFRESH MATERIALIZED VIEW CONCURRENTLY</command> as it requires
+      a populated materialized view.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index e4ed3748f9..96e7b81966 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -331,18 +331,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* An existing materialized view can be replaced. */
 		if (is_matview && into->replace)
 		{
-			RefreshMatViewStmt *refresh;
-
 			/* Change the relation to match the new query and other options. */
-			(void) create_ctas_nodata(query->targetList, into);
+			address = create_ctas_nodata(query->targetList, into);
 
-			/* Refresh the materialized view with a fake statement. */
-			refresh = makeNode(RefreshMatViewStmt);
-			refresh->relation = into->rel;
-			refresh->skipData = into->skipData;
-			refresh->concurrent = false;
+			/*
+			 * Refresh the materialized view with a fake statement unless we
+			 * must keep the old data.
+			 */
+			if (!into->keepData)
+			{
+				RefreshMatViewStmt *refresh;
+
+				refresh = makeNode(RefreshMatViewStmt);
+				refresh->relation = into->rel;
+				refresh->skipData = into->skipData;
+				refresh->concurrent = false;
+
+				address = ExecRefreshMatView(refresh, NULL, NULL);
+			}
 
-			return ExecRefreshMatView(refresh, NULL, NULL);
+			return address;
 		}
 
 		return InvalidObjectAddress;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 4b939ea7ca..e45ebb24f8 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4808,6 +4808,22 @@ CreateMatViewStmt:
 					$7->replace = true;
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt WITH OLD DATA_P
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = false;
+					$7->keepData = true;
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 4b0ee5d10d..ae84cb522e 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	Node	   *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		keepData;		/* true for WITH OLD DATA */
 	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index cefd0d442c..47dfd88bff 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -751,6 +751,23 @@ SELECT * FROM mvtest_replace;
  3
 (1 row)
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 5
+(1 row)
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -905,3 +922,14 @@ ERROR:  syntax error at or near "NOT"
 LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
                                                ^
 DROP MATERIALIZED VIEW mvtest_replace;
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a  
+----
+ 17
+(1 row)
+
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index c12f0243c9..b268237c24 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -338,6 +338,14 @@ SELECT * FROM mvtest_replace; -- error: not populated
 REFRESH MATERIALIZED VIEW mvtest_replace;
 SELECT * FROM mvtest_replace;
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -422,3 +430,10 @@ CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
   SELECT 1 AS a;
 
 DROP MATERIALIZED VIEW mvtest_replace;
+
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
-- 
2.46.0

From eefed7938bc1511a1ae998f67c67661c366484ec Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 21 May 2024 18:35:47 +0200
Subject: [PATCH v4 1/3] Add CREATE OR REPLACE MATERIALIZED VIEW

---
 .../sgml/ref/create_materialized_view.sgml    |  15 +-
 src/backend/commands/createas.c               | 207 ++++++++++++++----
 src/backend/commands/tablecmds.c              |   8 +-
 src/backend/commands/view.c                   | 106 ++++++---
 src/backend/parser/gram.y                     |  15 ++
 src/bin/psql/tab-complete.in.c                |  15 +-
 src/include/commands/view.h                   |   3 +
 src/include/nodes/parsenodes.h                |   2 +-
 src/include/nodes/primnodes.h                 |   1 +
 src/test/regress/expected/matview.out         | 191 ++++++++++++++++
 src/test/regress/sql/matview.sql              | 108 +++++++++
 11 files changed, 582 insertions(+), 89 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 62d897931c..5e03320eb7 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
+CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ USING <replaceable class="parameter">method</replaceable> ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
@@ -60,6 +60,17 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>OR REPLACE</literal></term>
+    <listitem>
+     <para>
+      Replaces a materialized view if it already exists.
+      Specifying <literal>OR REPLACE</literal> together with
+      <literal>IF NOT EXISTS</literal> is an error.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
@@ -67,7 +78,7 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
       Do not throw an error if a materialized view with the same name already
       exists. A notice is issued in this case.  Note that there is no guarantee
       that the existing materialized view is anything like the one that would
-      have been created.
+      have been created, unless you use <literal>OR REPLACE</literal> instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 5c92e48a56..d4bc5e5c08 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -79,55 +79,151 @@ static void intorel_destroy(DestReceiver *self);
 static ObjectAddress
 create_ctas_internal(List *attrList, IntoClause *into)
 {
-	CreateStmt *create = makeNode(CreateStmt);
-	bool		is_matview;
+	bool		is_matview,
+				replace = false;
 	char		relkind;
-	Datum		toast_options;
-	const char *const validnsps[] = HEAP_RELOPT_NAMESPACES;
+	Oid			matviewOid = InvalidOid;
 	ObjectAddress intoRelationAddr;
 
 	/* This code supports both CREATE TABLE AS and CREATE MATERIALIZED VIEW */
 	is_matview = (into->viewQuery != NULL);
 	relkind = is_matview ? RELKIND_MATVIEW : RELKIND_RELATION;
 
-	/*
-	 * Create the target relation by faking up a CREATE TABLE parsetree and
-	 * passing it to DefineRelation.
-	 */
-	create->relation = into->rel;
-	create->tableElts = attrList;
-	create->inhRelations = NIL;
-	create->ofTypename = NULL;
-	create->constraints = NIL;
-	create->options = into->options;
-	create->oncommit = into->onCommit;
-	create->tablespacename = into->tableSpaceName;
-	create->if_not_exists = false;
-	create->accessMethod = into->accessMethod;
+	/* Check if an existing materialized view needs to be replaced. */
+	if (is_matview)
+	{
+		LOCKMODE	lockmode;
 
-	/*
-	 * Create the relation.  (This will error out if there's an existing view,
-	 * so we don't need more code to complain if "replace" is false.)
-	 */
-	intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL, NULL);
+		lockmode = into->replace ? AccessExclusiveLock : NoLock;
+		(void) RangeVarGetAndCheckCreationNamespace(into->rel, lockmode,
+													&matviewOid);
+		replace = OidIsValid(matviewOid) && into->replace;
+	}
 
-	/*
-	 * If necessary, create a TOAST table for the target table.  Note that
-	 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
-	 * that the TOAST table will be visible for insertion.
-	 */
-	CommandCounterIncrement();
+	if (is_matview && replace)
+	{
+		Relation	rel;
+		List	   *atcmds = NIL;
+		AlterTableCmd *atcmd;
+		TupleDesc	descriptor;
+
+		rel = relation_open(matviewOid, NoLock);
+
+		if (rel->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					errmsg("\"%s\" is not a materialized view",
+						   RelationGetRelationName(rel)));
+
+		CheckTableNotInUse(rel, "CREATE OR REPLACE MATERIALIZED VIEW");
+
+		descriptor = BuildDescForRelation(attrList);
+		checkViewColumns(descriptor, rel->rd_att, true);
+
+		/* Add new attributes via ALTER TABLE. */
+		if (list_length(attrList) > rel->rd_att->natts)
+		{
+			ListCell   *c;
+			int			skip = rel->rd_att->natts;
+
+			foreach(c, attrList)
+			{
+				if (skip > 0)
+				{
+					skip--;
+					continue;
+				}
+				atcmd = makeNode(AlterTableCmd);
+				atcmd->subtype = AT_AddColumnToView;
+				atcmd->def = (Node *) lfirst(c);
+				atcmds = lappend(atcmds, atcmd);
+			}
+		}
+
+		/* Set access method via ALTER TABLE. */
+		if (into->accessMethod != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetAccessMethod;
+			atcmd->name = into->accessMethod;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set tablespace via ALTER TABLE. */
+		if (into->tableSpaceName != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetTableSpace;
+			atcmd->name = into->tableSpaceName;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set storage parameters via ALTER TABLE. */
+		if (into->options != NIL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_ReplaceRelOptions;
+			atcmd->def = (Node *) into->options;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		if (atcmds != NIL)
+		{
+			AlterTableInternal(matviewOid, atcmds, true);
+			CommandCounterIncrement();
+		}
+
+		relation_close(rel, NoLock);
+
+		ObjectAddressSet(intoRelationAddr, RelationRelationId, matviewOid);
+	}
+	else
+	{
+		CreateStmt *create = makeNode(CreateStmt);
+		Datum		toast_options;
+		const static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+
+		/*
+		 * Create the target relation by faking up a CREATE TABLE parsetree
+		 * and passing it to DefineRelation.
+		 */
+		create->relation = into->rel;
+		create->tableElts = attrList;
+		create->inhRelations = NIL;
+		create->ofTypename = NULL;
+		create->constraints = NIL;
+		create->options = into->options;
+		create->oncommit = into->onCommit;
+		create->tablespacename = into->tableSpaceName;
+		create->if_not_exists = false;
+		create->accessMethod = into->accessMethod;
+
+		/*
+		 * Create the relation.  (This will error out if there's an existing
+		 * view, so we don't need more code to complain if "replace" is
+		 * false.)
+		 */
+		intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL,
+										  NULL);
 
-	/* parse and validate reloptions for the toast table */
-	toast_options = transformRelOptions((Datum) 0,
-										create->options,
-										"toast",
-										validnsps,
-										true, false);
+		/*
+		 * If necessary, create a TOAST table for the target table.  Note that
+		 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
+		 * that the TOAST table will be visible for insertion.
+		 */
+		CommandCounterIncrement();
+
+		/* parse and validate reloptions for the toast table */
+		toast_options = transformRelOptions((Datum) 0,
+											create->options,
+											"toast",
+											validnsps,
+											true, false);
 
-	(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
+		(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
 
-	NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+		NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+	}
 
 	/* Create the "view" part of a materialized view. */
 	if (is_matview)
@@ -135,7 +231,7 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* StoreViewQuery scribbles on tree, so make a copy */
 		Query	   *query = copyObject(into->viewQuery);
 
-		StoreViewQuery(intoRelationAddr.objectId, query, false);
+		StoreViewQuery(intoRelationAddr.objectId, query, replace);
 		CommandCounterIncrement();
 	}
 
@@ -232,7 +328,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 
 	/* Check if the relation exists or not */
 	if (CreateTableAsRelExists(stmt))
+	{
+		/* An existing materialized view can be replaced. */
+		if (is_matview && into->replace)
+		{
+			RefreshMatViewStmt *refresh;
+
+			/* Change the relation to match the new query and other options. */
+			(void) create_ctas_nodata(query->targetList, into);
+
+			/* Refresh the materialized view with a fake statement. */
+			refresh = makeNode(RefreshMatViewStmt);
+			refresh->relation = into->rel;
+			refresh->skipData = into->skipData;
+			refresh->concurrent = false;
+
+			return ExecRefreshMatView(refresh, NULL, NULL);
+		}
+
 		return InvalidObjectAddress;
+	}
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -400,14 +515,15 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 	oldrelid = get_relname_relid(into->rel->relname, nspid);
 	if (OidIsValid(oldrelid))
 	{
-		if (!ctas->if_not_exists)
+		if (!ctas->if_not_exists && !into->replace)
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_TABLE),
 					 errmsg("relation \"%s\" already exists",
 							into->rel->relname)));
 
 		/*
-		 * The relation exists and IF NOT EXISTS has been specified.
+		 * The relation exists and IF NOT EXISTS or OR REPLACE has been
+		 * specified.
 		 *
 		 * If we are in an extension script, insist that the pre-existing
 		 * object be a member of the extension, to avoid security risks.
@@ -415,11 +531,12 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 		ObjectAddressSet(address, RelationRelationId, oldrelid);
 		checkMembershipInCurrentExtension(&address);
 
-		/* OK to skip */
-		ereport(NOTICE,
-				(errcode(ERRCODE_DUPLICATE_TABLE),
-				 errmsg("relation \"%s\" already exists, skipping",
-						into->rel->relname)));
+		if (ctas->if_not_exists)
+			/* OK to skip */
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							into->rel->relname)));
 		return true;
 	}
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 4345b96de5..436232bcf2 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4516,7 +4516,7 @@ AlterTableGetLockLevel(List *cmds)
 				 * Subcommands that may be visible to concurrent SELECTs
 				 */
 			case AT_DropColumn: /* change visible to SELECT */
-			case AT_AddColumnToView:	/* CREATE VIEW */
+			case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			case AT_DropOids:	/* used to equiv to DropColumn */
 			case AT_EnableAlwaysRule:	/* may change SELECT rules */
 			case AT_EnableReplicaRule:	/* may change SELECT rules */
@@ -4820,8 +4820,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
-			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW);
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
+			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW | ATT_MATVIEW);
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, true, cmd,
 							lockmode, context);
 			/* Recursion occurs during execution phase */
@@ -5252,7 +5252,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 	switch (cmd->subtype)
 	{
 		case AT_AddColumn:		/* ADD COLUMN */
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			address = ATExecAddColumn(wqueue, tab, rel, &cmd,
 									  cmd->recurse, false,
 									  lockmode, cur_pass, context);
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index 2bd49eb55e..65b9b2e9bb 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -30,8 +30,6 @@
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 
-static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
-
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -129,7 +127,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		 * column list.
 		 */
 		descriptor = BuildDescForRelation(attrList);
-		checkViewColumns(descriptor, rel->rd_att);
+		checkViewColumns(descriptor, rel->rd_att, false);
 
 		/*
 		 * If new attributes have been added, we must add pg_attribute entries
@@ -263,15 +261,22 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
  * added to generate specific complaints.  Also, we allow the new view to have
  * more columns than the old.
  */
-static void
-checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
+void
+checkViewColumns(TupleDesc newdesc, TupleDesc olddesc, bool is_matview)
 {
 	int			i;
 
 	if (newdesc->natts < olddesc->natts)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot drop columns from view")));
+	{
+		if (is_matview)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot drop columns from materialized view"));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot drop columns from view")));
+	}
 
 	for (i = 0; i < olddesc->natts; i++)
 	{
@@ -280,17 +285,34 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 
 		/* XXX msg not right, but we don't support DROP COL on view anyway */
 		if (newattr->attisdropped != oldattr->attisdropped)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot drop columns from view")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot drop columns from materialized view"));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot drop columns from view")));
+		}
 
 		if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							NameStr(newattr->attname)),
-					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change name of materialized view column \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   NameStr(newattr->attname)),
+						errhint("Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead."));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change name of view column \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								NameStr(newattr->attname)),
+						 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		}
 
 		/*
 		 * We cannot allow type, typmod, or collation to change, since these
@@ -299,26 +321,48 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 		 */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change data type of view column \"%s\" from %s to %s",
-							NameStr(oldattr->attname),
-							format_type_with_typemod(oldattr->atttypid,
-													 oldattr->atttypmod),
-							format_type_with_typemod(newattr->atttypid,
-													 newattr->atttypmod))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change data type of materialized view column \"%s\" from %s to %s",
+							   NameStr(oldattr->attname),
+							   format_type_with_typemod(oldattr->atttypid,
+														oldattr->atttypmod),
+							   format_type_with_typemod(newattr->atttypid,
+														newattr->atttypmod)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change data type of view column \"%s\" from %s to %s",
+								NameStr(oldattr->attname),
+								format_type_with_typemod(oldattr->atttypid,
+														 oldattr->atttypmod),
+								format_type_with_typemod(newattr->atttypid,
+														 newattr->atttypmod))));
+		}
 
 		/*
 		 * At this point, attcollations should be both valid or both invalid,
 		 * so applying get_collation_name unconditionally should be fine.
 		 */
 		if (newattr->attcollation != oldattr->attcollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							get_collation_name(oldattr->attcollation),
-							get_collation_name(newattr->attcollation))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change collation of materialized view column \"%s\" from \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   get_collation_name(oldattr->attcollation),
+							   get_collation_name(newattr->attcollation)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								get_collation_name(oldattr->attcollation),
+								get_collation_name(newattr->attcollation))));
+		}
 	}
 
 	/*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index dd458182f0..6b32233127 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4809,6 +4809,21 @@ CreateMatViewStmt:
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = !($10);
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 1be0056af7..122e44267e 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -2144,7 +2144,7 @@ match_previous_words(int pattern_id,
 	/* complete with something you can create or replace */
 	else if (TailMatches("CREATE", "OR", "REPLACE"))
 		COMPLETE_WITH("FUNCTION", "PROCEDURE", "LANGUAGE", "RULE", "VIEW",
-					  "AGGREGATE", "TRANSFORM", "TRIGGER");
+					  "AGGREGATE", "TRANSFORM", "TRIGGER", "MATERIALIZED VIEW");
 
 /* DROP, but not DROP embedded in other commands */
 	/* complete with something you can drop */
@@ -3964,13 +3964,16 @@ match_previous_words(int pattern_id,
 		COMPLETE_WITH("SELECT");
 
 /* CREATE MATERIALIZED VIEW */
-	else if (Matches("CREATE", "MATERIALIZED"))
+	else if (Matches("CREATE", "MATERIALIZED") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED"))
 		COMPLETE_WITH("VIEW");
-	/* Complete CREATE MATERIALIZED VIEW <name> with AS */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> with AS */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("AS");
-	/* Complete "CREATE MATERIALIZED VIEW <sth> AS with "SELECT" */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS"))
+	/* Complete "CREATE [ OR REPLACE ] MATERIALIZED VIEW <sth> AS with "SELECT" */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "AS"))
 		COMPLETE_WITH("SELECT");
 
 /* CREATE EVENT TRIGGER */
diff --git a/src/include/commands/view.h b/src/include/commands/view.h
index d2d8588989..7eacdaaceb 100644
--- a/src/include/commands/view.h
+++ b/src/include/commands/view.h
@@ -22,4 +22,7 @@ extern ObjectAddress DefineView(ViewStmt *stmt, const char *queryString,
 
 extern void StoreViewQuery(Oid viewOid, Query *viewParse, bool replace);
 
+extern void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc,
+							 bool is_matview);
+
 #endif							/* VIEW_H */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index b40b661ec8..b71db02c24 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2358,7 +2358,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
-	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
+	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE [MATERIALIZED] VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_CookedColumnDefault,		/* add a pre-cooked column default */
 	AT_DropNotNull,				/* alter column drop not null */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index b0ef1952e8..533fa847ab 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 038ab73517..e2e2a13396 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -694,3 +694,194 @@ NOTICE:  relation "matview_ine_tab" already exists, skipping
 (0 rows)
 
 DROP MATERIALIZED VIEW matview_ine_tab;
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+NOTICE:  materialized view "mvtest_replace" does not exist, skipping
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 1
+(1 row)
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 2
+(1 row)
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+ERROR:  materialized view "mvtest_replace" has not been populated
+HINT:  Use the REFRESH MATERIALIZED VIEW command.
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 4 | 1
+(1 row)
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 4 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     |   reloptions    |     spcname      | amname 
+---+---+----------------+-----------------+------------------+--------
+ 5 | 1 | mvtest_replace | {fillfactor=50} | regress_tblspace | heap2
+(1 row)
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+ a | b | a | b 
+---+---+---+---
+ 6 | 1 | 6 | 1
+(1 row)
+
+DROP VIEW mvtest_replace_v;
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+RESET enable_seqscan;
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+ERROR:  cannot change data type of materialized view column "b" from integer to text
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+ERROR:  cannot change name of materialized view column "b" to "b2"
+HINT:  Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead.
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+ERROR:  cannot change collation of materialized view column "c" from "C" to "POSIX"
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+ERROR:  cannot drop columns from materialized view
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+ERROR:  "mvtest_not_mv" is not a materialized view
+DROP VIEW mvtest_not_mv;
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+ERROR:  syntax error at or near "NOT"
+LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
+                                               ^
+DROP MATERIALIZED VIEW mvtest_replace;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index b74ee305e0..c12f0243c9 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -314,3 +314,111 @@ EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
 DROP MATERIALIZED VIEW matview_ine_tab;
+
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+DROP VIEW mvtest_replace_v;
+
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+SELECT * FROM mvtest_replace;
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+DROP VIEW mvtest_not_mv;
+
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+
+DROP MATERIALIZED VIEW mvtest_replace;
-- 
2.47.0

From ce6d3bbdac073b4750745120f9a754c30bd57b66 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 28 May 2024 02:19:53 +0200
Subject: [PATCH v4 2/3] Deprecate CREATE MATERIALIZED VIEW IF NOT EXISTS

---
 src/backend/parser/gram.y                     | 14 ++++++
 .../expected/test_extensions.out              | 45 +++++++++++++++++++
 src/test/regress/expected/matview.out         | 20 +++++++++
 3 files changed, 79 insertions(+)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 6b32233127..dadc6b630a 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4808,6 +4808,20 @@ CreateMatViewStmt:
 					$8->rel->relpersistence = $2;
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
+
+					if (ctas->into->rel->schemaname)
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.%s.",
+											ctas->into->rel->schemaname,
+											ctas->into->rel->relname),
+									parser_errposition(@1));
+					else
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.",
+											ctas->into->rel->relname),
+									parser_errposition(@1));
 				}
 		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
 				{
diff --git a/src/test/modules/test_extensions/expected/test_extensions.out b/src/test/modules/test_extensions/expected/test_extensions.out
index d5388a1fec..9a1e0f7658 100644
--- a/src/test/modules/test_extensions/expected/test_extensions.out
+++ b/src/test/modules/test_extensions/expected/test_extensions.out
@@ -404,6 +404,11 @@ Objects in extension "test_ext_cor"
 CREATE COLLATION ext_cine_coll
   ( LC_COLLATE = "C", LC_CTYPE = "C" );
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  collation ext_cine_coll is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE COLLATION IF NOT EXISTS ext_cine_coll
@@ -412,6 +417,11 @@ extension script file "test_ext_cine--1.0.sql", near line 10
 DROP COLLATION ext_cine_coll;
 CREATE MATERIALIZED VIEW ext_cine_mv AS SELECT 11 AS f1;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  materialized view ext_cine_mv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1"
@@ -420,6 +430,11 @@ DROP MATERIALIZED VIEW ext_cine_mv;
 CREATE FOREIGN DATA WRAPPER dummy;
 CREATE SERVER ext_cine_srv FOREIGN DATA WRAPPER dummy;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  server ext_cine_srv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SERVER IF NOT EXISTS ext_cine_srv FOREIGN DATA WRAPPER ext_cine_fdw"
@@ -427,6 +442,11 @@ extension script file "test_ext_cine--1.0.sql", near line 17
 DROP SERVER ext_cine_srv;
 CREATE SCHEMA ext_cine_schema;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  schema ext_cine_schema is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SCHEMA IF NOT EXISTS ext_cine_schema"
@@ -434,6 +454,11 @@ extension script file "test_ext_cine--1.0.sql", near line 19
 DROP SCHEMA ext_cine_schema;
 CREATE SEQUENCE ext_cine_seq;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  sequence ext_cine_seq is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SEQUENCE IF NOT EXISTS ext_cine_seq"
@@ -441,6 +466,11 @@ extension script file "test_ext_cine--1.0.sql", near line 21
 DROP SEQUENCE ext_cine_seq;
 CREATE TABLE ext_cine_tab1 (x int);
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  table ext_cine_tab1 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE TABLE IF NOT EXISTS ext_cine_tab1 (x int)"
@@ -448,12 +478,22 @@ extension script file "test_ext_cine--1.0.sql", near line 23
 DROP TABLE ext_cine_tab1;
 CREATE TABLE ext_cine_tab2 AS SELECT 42 AS y;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  table ext_cine_tab2 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE TABLE IF NOT EXISTS ext_cine_tab2 AS SELECT 42 AS y"
 extension script file "test_ext_cine--1.0.sql", near line 25
 DROP TABLE ext_cine_tab2;
 CREATE EXTENSION test_ext_cine;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
@@ -475,6 +515,11 @@ Objects in extension "test_ext_cine"
 (14 rows)
 
 ALTER EXTENSION test_ext_cine UPDATE TO '1.1';
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index e2e2a13396..cefd0d442c 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -565,6 +565,10 @@ CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 ERROR:  relation "mvtest_mv_foo" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELE...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW mvtest_mv_foo.
 NOTICE:  relation "mvtest_mv_foo" already exists, skipping
 CREATE UNIQUE INDEX ON mvtest_mv_foo (i);
 RESET ROLE;
@@ -662,12 +666,20 @@ CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 CREATE MATERIALIZED VIEW matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW matview_ine_tab AS
@@ -676,6 +688,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
@@ -688,6 +704,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
-- 
2.47.0

From 33fe1e0d676fb4fdde43ed687dc66e98f7f8b6d5 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Fri, 26 Jul 2024 23:33:15 +0200
Subject: [PATCH v4 3/3] Replace matview WITH OLD DATA

---
 .../sgml/ref/create_materialized_view.sgml    | 16 +++++++++--
 src/backend/commands/createas.c               | 26 +++++++++++------
 src/backend/parser/gram.y                     | 16 +++++++++++
 src/include/nodes/primnodes.h                 |  1 +
 src/test/regress/expected/matview.out         | 28 +++++++++++++++++++
 src/test/regress/sql/matview.sql              | 15 ++++++++++
 6 files changed, 90 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 5e03320eb7..1352e9de40 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -27,7 +27,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     AS <replaceable>query</replaceable>
-    [ WITH [ NO ] DATA ]
+    [ WITH [ NO | OLD ] DATA ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -37,7 +37,8 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
   <para>
    <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
    a query.  The query is executed and used to populate the view at the time
-   the command is issued (unless <command>WITH NO DATA</command> is used) and may be
+   the command is issued (unless <command>WITH NO DATA</command> or
+   <command>WITH OLD DATA</command> is used) and may be
    refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
   </para>
 
@@ -162,7 +163,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
    </varlistentry>
 
    <varlistentry>
-    <term><literal>WITH [ NO ] DATA</literal></term>
+    <term><literal>WITH [ NO | OLD ] DATA</literal></term>
     <listitem>
      <para>
       This clause specifies whether or not the materialized view should be
@@ -170,6 +171,15 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
       flagged as unscannable and cannot be queried until <command>REFRESH
       MATERIALIZED VIEW</command> is used.
      </para>
+
+     <para>
+      The form <command>WITH OLD DATA</command> keeps the already stored data
+      when replacing an existing materialized view to keep it populated.  For
+      newly created materialized views, this has the same effect as
+      <command>WITH DATA</command>.  Use this form if you want to use
+      <command>REFRESH MATERIALIZED VIEW CONCURRENTLY</command> as it requires
+      a populated materialized view.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index d4bc5e5c08..8db000554c 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -332,18 +332,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* An existing materialized view can be replaced. */
 		if (is_matview && into->replace)
 		{
-			RefreshMatViewStmt *refresh;
-
 			/* Change the relation to match the new query and other options. */
-			(void) create_ctas_nodata(query->targetList, into);
+			address = create_ctas_nodata(query->targetList, into);
 
-			/* Refresh the materialized view with a fake statement. */
-			refresh = makeNode(RefreshMatViewStmt);
-			refresh->relation = into->rel;
-			refresh->skipData = into->skipData;
-			refresh->concurrent = false;
+			/*
+			 * Refresh the materialized view with a fake statement unless we
+			 * must keep the old data.
+			 */
+			if (!into->keepData)
+			{
+				RefreshMatViewStmt *refresh;
+
+				refresh = makeNode(RefreshMatViewStmt);
+				refresh->relation = into->rel;
+				refresh->skipData = into->skipData;
+				refresh->concurrent = false;
+
+				address = ExecRefreshMatView(refresh, NULL, NULL);
+			}
 
-			return ExecRefreshMatView(refresh, NULL, NULL);
+			return address;
 		}
 
 		return InvalidObjectAddress;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index dadc6b630a..1be1a95cd9 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4838,6 +4838,22 @@ CreateMatViewStmt:
 					$7->replace = true;
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt WITH OLD DATA_P
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = false;
+					$7->keepData = true;
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 533fa847ab..6fa3291c64 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		keepData;		/* true for WITH OLD DATA */
 	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index cefd0d442c..47dfd88bff 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -751,6 +751,23 @@ SELECT * FROM mvtest_replace;
  3
 (1 row)
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 5
+(1 row)
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -905,3 +922,14 @@ ERROR:  syntax error at or near "NOT"
 LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
                                                ^
 DROP MATERIALIZED VIEW mvtest_replace;
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a  
+----
+ 17
+(1 row)
+
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index c12f0243c9..b268237c24 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -338,6 +338,14 @@ SELECT * FROM mvtest_replace; -- error: not populated
 REFRESH MATERIALIZED VIEW mvtest_replace;
 SELECT * FROM mvtest_replace;
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -422,3 +430,10 @@ CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
   SELECT 1 AS a;
 
 DROP MATERIALIZED VIEW mvtest_replace;
+
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
-- 
2.47.0

From ac9bba0960f7a6fa507020400f1b4bcf4c9a25d3 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 21 May 2024 18:35:47 +0200
Subject: [PATCH v5 1/3] Add CREATE OR REPLACE MATERIALIZED VIEW

---
 .../sgml/ref/create_materialized_view.sgml    |  15 +-
 src/backend/commands/createas.c               | 207 ++++++++++++++----
 src/backend/commands/tablecmds.c              |   8 +-
 src/backend/commands/view.c                   | 106 ++++++---
 src/backend/parser/gram.y                     |  15 ++
 src/bin/psql/tab-complete.in.c                |  26 ++-
 src/include/commands/view.h                   |   3 +
 src/include/nodes/parsenodes.h                |   2 +-
 src/include/nodes/primnodes.h                 |   1 +
 src/test/regress/expected/matview.out         | 191 ++++++++++++++++
 src/test/regress/sql/matview.sql              | 108 +++++++++
 11 files changed, 589 insertions(+), 93 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 62d897931c..5e03320eb7 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
+CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ USING <replaceable class="parameter">method</replaceable> ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
@@ -60,6 +60,17 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>OR REPLACE</literal></term>
+    <listitem>
+     <para>
+      Replaces a materialized view if it already exists.
+      Specifying <literal>OR REPLACE</literal> together with
+      <literal>IF NOT EXISTS</literal> is an error.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
@@ -67,7 +78,7 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
       Do not throw an error if a materialized view with the same name already
       exists. A notice is issued in this case.  Note that there is no guarantee
       that the existing materialized view is anything like the one that would
-      have been created.
+      have been created, unless you use <literal>OR REPLACE</literal> instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 23cecd99c9..cba369114b 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -79,55 +79,151 @@ static void intorel_destroy(DestReceiver *self);
 static ObjectAddress
 create_ctas_internal(List *attrList, IntoClause *into)
 {
-	CreateStmt *create = makeNode(CreateStmt);
-	bool		is_matview;
+	bool		is_matview,
+				replace = false;
 	char		relkind;
-	Datum		toast_options;
-	const char *const validnsps[] = HEAP_RELOPT_NAMESPACES;
+	Oid			matviewOid = InvalidOid;
 	ObjectAddress intoRelationAddr;
 
 	/* This code supports both CREATE TABLE AS and CREATE MATERIALIZED VIEW */
 	is_matview = (into->viewQuery != NULL);
 	relkind = is_matview ? RELKIND_MATVIEW : RELKIND_RELATION;
 
-	/*
-	 * Create the target relation by faking up a CREATE TABLE parsetree and
-	 * passing it to DefineRelation.
-	 */
-	create->relation = into->rel;
-	create->tableElts = attrList;
-	create->inhRelations = NIL;
-	create->ofTypename = NULL;
-	create->constraints = NIL;
-	create->options = into->options;
-	create->oncommit = into->onCommit;
-	create->tablespacename = into->tableSpaceName;
-	create->if_not_exists = false;
-	create->accessMethod = into->accessMethod;
+	/* Check if an existing materialized view needs to be replaced. */
+	if (is_matview)
+	{
+		LOCKMODE	lockmode;
 
-	/*
-	 * Create the relation.  (This will error out if there's an existing view,
-	 * so we don't need more code to complain if "replace" is false.)
-	 */
-	intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL, NULL);
+		lockmode = into->replace ? AccessExclusiveLock : NoLock;
+		(void) RangeVarGetAndCheckCreationNamespace(into->rel, lockmode,
+													&matviewOid);
+		replace = OidIsValid(matviewOid) && into->replace;
+	}
 
-	/*
-	 * If necessary, create a TOAST table for the target table.  Note that
-	 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
-	 * that the TOAST table will be visible for insertion.
-	 */
-	CommandCounterIncrement();
+	if (is_matview && replace)
+	{
+		Relation	rel;
+		List	   *atcmds = NIL;
+		AlterTableCmd *atcmd;
+		TupleDesc	descriptor;
+
+		rel = relation_open(matviewOid, NoLock);
+
+		if (rel->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					errmsg("\"%s\" is not a materialized view",
+						   RelationGetRelationName(rel)));
+
+		CheckTableNotInUse(rel, "CREATE OR REPLACE MATERIALIZED VIEW");
+
+		descriptor = BuildDescForRelation(attrList);
+		checkViewColumns(descriptor, rel->rd_att, true);
+
+		/* Add new attributes via ALTER TABLE. */
+		if (list_length(attrList) > rel->rd_att->natts)
+		{
+			ListCell   *c;
+			int			skip = rel->rd_att->natts;
+
+			foreach(c, attrList)
+			{
+				if (skip > 0)
+				{
+					skip--;
+					continue;
+				}
+				atcmd = makeNode(AlterTableCmd);
+				atcmd->subtype = AT_AddColumnToView;
+				atcmd->def = (Node *) lfirst(c);
+				atcmds = lappend(atcmds, atcmd);
+			}
+		}
+
+		/* Set access method via ALTER TABLE. */
+		if (into->accessMethod != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetAccessMethod;
+			atcmd->name = into->accessMethod;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set tablespace via ALTER TABLE. */
+		if (into->tableSpaceName != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetTableSpace;
+			atcmd->name = into->tableSpaceName;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set storage parameters via ALTER TABLE. */
+		if (into->options != NIL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_ReplaceRelOptions;
+			atcmd->def = (Node *) into->options;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		if (atcmds != NIL)
+		{
+			AlterTableInternal(matviewOid, atcmds, true);
+			CommandCounterIncrement();
+		}
+
+		relation_close(rel, NoLock);
+
+		ObjectAddressSet(intoRelationAddr, RelationRelationId, matviewOid);
+	}
+	else
+	{
+		CreateStmt *create = makeNode(CreateStmt);
+		Datum		toast_options;
+		const static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+
+		/*
+		 * Create the target relation by faking up a CREATE TABLE parsetree
+		 * and passing it to DefineRelation.
+		 */
+		create->relation = into->rel;
+		create->tableElts = attrList;
+		create->inhRelations = NIL;
+		create->ofTypename = NULL;
+		create->constraints = NIL;
+		create->options = into->options;
+		create->oncommit = into->onCommit;
+		create->tablespacename = into->tableSpaceName;
+		create->if_not_exists = false;
+		create->accessMethod = into->accessMethod;
+
+		/*
+		 * Create the relation.  (This will error out if there's an existing
+		 * view, so we don't need more code to complain if "replace" is
+		 * false.)
+		 */
+		intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL,
+										  NULL);
 
-	/* parse and validate reloptions for the toast table */
-	toast_options = transformRelOptions((Datum) 0,
-										create->options,
-										"toast",
-										validnsps,
-										true, false);
+		/*
+		 * If necessary, create a TOAST table for the target table.  Note that
+		 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
+		 * that the TOAST table will be visible for insertion.
+		 */
+		CommandCounterIncrement();
+
+		/* parse and validate reloptions for the toast table */
+		toast_options = transformRelOptions((Datum) 0,
+											create->options,
+											"toast",
+											validnsps,
+											true, false);
 
-	(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
+		(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
 
-	NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+		NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+	}
 
 	/* Create the "view" part of a materialized view. */
 	if (is_matview)
@@ -135,7 +231,7 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* StoreViewQuery scribbles on tree, so make a copy */
 		Query	   *query = copyObject(into->viewQuery);
 
-		StoreViewQuery(intoRelationAddr.objectId, query, false);
+		StoreViewQuery(intoRelationAddr.objectId, query, replace);
 		CommandCounterIncrement();
 	}
 
@@ -232,7 +328,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 
 	/* Check if the relation exists or not */
 	if (CreateTableAsRelExists(stmt))
+	{
+		/* An existing materialized view can be replaced. */
+		if (is_matview && into->replace)
+		{
+			RefreshMatViewStmt *refresh;
+
+			/* Change the relation to match the new query and other options. */
+			(void) create_ctas_nodata(query->targetList, into);
+
+			/* Refresh the materialized view with a fake statement. */
+			refresh = makeNode(RefreshMatViewStmt);
+			refresh->relation = into->rel;
+			refresh->skipData = into->skipData;
+			refresh->concurrent = false;
+
+			return ExecRefreshMatView(refresh, NULL, NULL);
+		}
+
 		return InvalidObjectAddress;
+	}
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -400,14 +515,15 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 	oldrelid = get_relname_relid(into->rel->relname, nspid);
 	if (OidIsValid(oldrelid))
 	{
-		if (!ctas->if_not_exists)
+		if (!ctas->if_not_exists && !into->replace)
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_TABLE),
 					 errmsg("relation \"%s\" already exists",
 							into->rel->relname)));
 
 		/*
-		 * The relation exists and IF NOT EXISTS has been specified.
+		 * The relation exists and IF NOT EXISTS or OR REPLACE has been
+		 * specified.
 		 *
 		 * If we are in an extension script, insist that the pre-existing
 		 * object be a member of the extension, to avoid security risks.
@@ -415,11 +531,12 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 		ObjectAddressSet(address, RelationRelationId, oldrelid);
 		checkMembershipInCurrentExtension(&address);
 
-		/* OK to skip */
-		ereport(NOTICE,
-				(errcode(ERRCODE_DUPLICATE_TABLE),
-				 errmsg("relation \"%s\" already exists, skipping",
-						into->rel->relname)));
+		if (ctas->if_not_exists)
+			/* OK to skip */
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							into->rel->relname)));
 		return true;
 	}
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 4fc54bd6eb..12ba984a05 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4589,7 +4589,7 @@ AlterTableGetLockLevel(List *cmds)
 				 * Subcommands that may be visible to concurrent SELECTs
 				 */
 			case AT_DropColumn: /* change visible to SELECT */
-			case AT_AddColumnToView:	/* CREATE VIEW */
+			case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			case AT_DropOids:	/* used to equiv to DropColumn */
 			case AT_EnableAlwaysRule:	/* may change SELECT rules */
 			case AT_EnableReplicaRule:	/* may change SELECT rules */
@@ -4884,8 +4884,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
-			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW);
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
+			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW | ATT_MATVIEW);
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, true, cmd,
 							lockmode, context);
 			/* Recursion occurs during execution phase */
@@ -5314,7 +5314,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 	switch (cmd->subtype)
 	{
 		case AT_AddColumn:		/* ADD COLUMN */
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			address = ATExecAddColumn(wqueue, tab, rel, &cmd,
 									  cmd->recurse, false,
 									  lockmode, cur_pass, context);
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index 6f0301555e..53d4cacc4c 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -30,8 +30,6 @@
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 
-static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
-
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -129,7 +127,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		 * column list.
 		 */
 		descriptor = BuildDescForRelation(attrList);
-		checkViewColumns(descriptor, rel->rd_att);
+		checkViewColumns(descriptor, rel->rd_att, false);
 
 		/*
 		 * If new attributes have been added, we must add pg_attribute entries
@@ -263,15 +261,22 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
  * added to generate specific complaints.  Also, we allow the new view to have
  * more columns than the old.
  */
-static void
-checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
+void
+checkViewColumns(TupleDesc newdesc, TupleDesc olddesc, bool is_matview)
 {
 	int			i;
 
 	if (newdesc->natts < olddesc->natts)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot drop columns from view")));
+	{
+		if (is_matview)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot drop columns from materialized view"));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot drop columns from view")));
+	}
 
 	for (i = 0; i < olddesc->natts; i++)
 	{
@@ -280,17 +285,34 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 
 		/* XXX msg not right, but we don't support DROP COL on view anyway */
 		if (newattr->attisdropped != oldattr->attisdropped)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot drop columns from view")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot drop columns from materialized view"));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot drop columns from view")));
+		}
 
 		if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							NameStr(newattr->attname)),
-					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change name of materialized view column \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   NameStr(newattr->attname)),
+						errhint("Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead."));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change name of view column \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								NameStr(newattr->attname)),
+						 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		}
 
 		/*
 		 * We cannot allow type, typmod, or collation to change, since these
@@ -299,26 +321,48 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 		 */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change data type of view column \"%s\" from %s to %s",
-							NameStr(oldattr->attname),
-							format_type_with_typemod(oldattr->atttypid,
-													 oldattr->atttypmod),
-							format_type_with_typemod(newattr->atttypid,
-													 newattr->atttypmod))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change data type of materialized view column \"%s\" from %s to %s",
+							   NameStr(oldattr->attname),
+							   format_type_with_typemod(oldattr->atttypid,
+														oldattr->atttypmod),
+							   format_type_with_typemod(newattr->atttypid,
+														newattr->atttypmod)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change data type of view column \"%s\" from %s to %s",
+								NameStr(oldattr->attname),
+								format_type_with_typemod(oldattr->atttypid,
+														 oldattr->atttypmod),
+								format_type_with_typemod(newattr->atttypid,
+														 newattr->atttypmod))));
+		}
 
 		/*
 		 * At this point, attcollations should be both valid or both invalid,
 		 * so applying get_collation_name unconditionally should be fine.
 		 */
 		if (newattr->attcollation != oldattr->attcollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							get_collation_name(oldattr->attcollation),
-							get_collation_name(newattr->attcollation))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change collation of materialized view column \"%s\" from \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   get_collation_name(oldattr->attcollation),
+							   get_collation_name(newattr->attcollation)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								get_collation_name(oldattr->attcollation),
+								get_collation_name(newattr->attcollation))));
+		}
 	}
 
 	/*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 6079de70e0..c917c11f9e 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4854,6 +4854,21 @@ CreateMatViewStmt:
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = !($10);
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 81cbf10aa2..dd72c617d5 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -2144,7 +2144,7 @@ match_previous_words(int pattern_id,
 	/* complete with something you can create or replace */
 	else if (TailMatches("CREATE", "OR", "REPLACE"))
 		COMPLETE_WITH("FUNCTION", "PROCEDURE", "LANGUAGE", "RULE", "VIEW",
-					  "AGGREGATE", "TRANSFORM", "TRIGGER");
+					  "AGGREGATE", "TRANSFORM", "TRIGGER", "MATERIALIZED VIEW");
 
 /* DROP, but not DROP embedded in other commands */
 	/* complete with something you can drop */
@@ -3979,28 +3979,34 @@ match_previous_words(int pattern_id,
 		COMPLETE_WITH("SELECT");
 
 /* CREATE MATERIALIZED VIEW */
-	else if (Matches("CREATE", "MATERIALIZED"))
+	else if (Matches("CREATE", "MATERIALIZED") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED"))
 		COMPLETE_WITH("VIEW");
-	/* Complete CREATE MATERIALIZED VIEW <name> with AS or USING */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> with AS or USING */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("AS", "USING");
 
 	/*
-	 * Complete CREATE MATERIALIZED VIEW <name> USING with list of access
+	 * Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> USING with list of access
 	 * methods
 	 */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING"))
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_table_access_methods);
-	/* Complete CREATE MATERIALIZED VIEW <name> USING <access method> with AS */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> USING <access method> with AS */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny))
 		COMPLETE_WITH("AS");
 
 	/*
-	 * Complete CREATE MATERIALIZED VIEW <name> [USING <access method> ] AS
+	 * Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> [USING <access method> ] AS
 	 * with "SELECT"
 	 */
 	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
-			 Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS"))
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
+			 Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS"))
 		COMPLETE_WITH("SELECT");
 
 /* CREATE EVENT TRIGGER */
diff --git a/src/include/commands/view.h b/src/include/commands/view.h
index c41f51b161..95290f0a1c 100644
--- a/src/include/commands/view.h
+++ b/src/include/commands/view.h
@@ -22,4 +22,7 @@ extern ObjectAddress DefineView(ViewStmt *stmt, const char *queryString,
 
 extern void StoreViewQuery(Oid viewOid, Query *viewParse, bool replace);
 
+extern void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc,
+							 bool is_matview);
+
 #endif							/* VIEW_H */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index b191eaaeca..f4c16e6a9e 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2358,7 +2358,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
-	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
+	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE [MATERIALIZED] VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_CookedColumnDefault,		/* add a pre-cooked column default */
 	AT_DropNotNull,				/* alter column drop not null */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 9c2957eb54..fce057a8ac 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 9eab51bc2a..71f6a0681d 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -694,3 +694,194 @@ NOTICE:  relation "matview_ine_tab" already exists, skipping
 (0 rows)
 
 DROP MATERIALIZED VIEW matview_ine_tab;
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+NOTICE:  materialized view "mvtest_replace" does not exist, skipping
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 1
+(1 row)
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 2
+(1 row)
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+ERROR:  materialized view "mvtest_replace" has not been populated
+HINT:  Use the REFRESH MATERIALIZED VIEW command.
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 4 | 1
+(1 row)
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 4 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     |   reloptions    |     spcname      | amname 
+---+---+----------------+-----------------+------------------+--------
+ 5 | 1 | mvtest_replace | {fillfactor=50} | regress_tblspace | heap2
+(1 row)
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+ a | b | a | b 
+---+---+---+---
+ 6 | 1 | 6 | 1
+(1 row)
+
+DROP VIEW mvtest_replace_v;
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+RESET enable_seqscan;
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+ERROR:  cannot change data type of materialized view column "b" from integer to text
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+ERROR:  cannot change name of materialized view column "b" to "b2"
+HINT:  Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead.
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+ERROR:  cannot change collation of materialized view column "c" from "C" to "POSIX"
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+ERROR:  cannot drop columns from materialized view
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+ERROR:  "mvtest_not_mv" is not a materialized view
+DROP VIEW mvtest_not_mv;
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+ERROR:  syntax error at or near "NOT"
+LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
+                                               ^
+DROP MATERIALIZED VIEW mvtest_replace;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index 6704eeae2d..d6a4dc4b85 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -314,3 +314,111 @@ EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
 DROP MATERIALIZED VIEW matview_ine_tab;
+
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+DROP VIEW mvtest_replace_v;
+
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+SELECT * FROM mvtest_replace;
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+DROP VIEW mvtest_not_mv;
+
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+
+DROP MATERIALIZED VIEW mvtest_replace;
-- 
2.48.0

From 2478cd438360a2fd5d74082c96b8feabd49ac593 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 28 May 2024 02:19:53 +0200
Subject: [PATCH v5 2/3] Deprecate CREATE MATERIALIZED VIEW IF NOT EXISTS

---
 src/backend/parser/gram.y                     | 14 ++++++
 .../expected/test_extensions.out              | 45 +++++++++++++++++++
 src/test/regress/expected/matview.out         | 20 +++++++++
 3 files changed, 79 insertions(+)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index c917c11f9e..cb5647dcb6 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4853,6 +4853,20 @@ CreateMatViewStmt:
 					$8->rel->relpersistence = $2;
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
+
+					if (ctas->into->rel->schemaname)
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.%s.",
+											ctas->into->rel->schemaname,
+											ctas->into->rel->relname),
+									parser_errposition(@1));
+					else
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.",
+											ctas->into->rel->relname),
+									parser_errposition(@1));
 				}
 		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
 				{
diff --git a/src/test/modules/test_extensions/expected/test_extensions.out b/src/test/modules/test_extensions/expected/test_extensions.out
index d5388a1fec..9a1e0f7658 100644
--- a/src/test/modules/test_extensions/expected/test_extensions.out
+++ b/src/test/modules/test_extensions/expected/test_extensions.out
@@ -404,6 +404,11 @@ Objects in extension "test_ext_cor"
 CREATE COLLATION ext_cine_coll
   ( LC_COLLATE = "C", LC_CTYPE = "C" );
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  collation ext_cine_coll is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE COLLATION IF NOT EXISTS ext_cine_coll
@@ -412,6 +417,11 @@ extension script file "test_ext_cine--1.0.sql", near line 10
 DROP COLLATION ext_cine_coll;
 CREATE MATERIALIZED VIEW ext_cine_mv AS SELECT 11 AS f1;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  materialized view ext_cine_mv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1"
@@ -420,6 +430,11 @@ DROP MATERIALIZED VIEW ext_cine_mv;
 CREATE FOREIGN DATA WRAPPER dummy;
 CREATE SERVER ext_cine_srv FOREIGN DATA WRAPPER dummy;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  server ext_cine_srv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SERVER IF NOT EXISTS ext_cine_srv FOREIGN DATA WRAPPER ext_cine_fdw"
@@ -427,6 +442,11 @@ extension script file "test_ext_cine--1.0.sql", near line 17
 DROP SERVER ext_cine_srv;
 CREATE SCHEMA ext_cine_schema;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  schema ext_cine_schema is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SCHEMA IF NOT EXISTS ext_cine_schema"
@@ -434,6 +454,11 @@ extension script file "test_ext_cine--1.0.sql", near line 19
 DROP SCHEMA ext_cine_schema;
 CREATE SEQUENCE ext_cine_seq;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  sequence ext_cine_seq is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SEQUENCE IF NOT EXISTS ext_cine_seq"
@@ -441,6 +466,11 @@ extension script file "test_ext_cine--1.0.sql", near line 21
 DROP SEQUENCE ext_cine_seq;
 CREATE TABLE ext_cine_tab1 (x int);
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  table ext_cine_tab1 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE TABLE IF NOT EXISTS ext_cine_tab1 (x int)"
@@ -448,12 +478,22 @@ extension script file "test_ext_cine--1.0.sql", near line 23
 DROP TABLE ext_cine_tab1;
 CREATE TABLE ext_cine_tab2 AS SELECT 42 AS y;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  table ext_cine_tab2 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE TABLE IF NOT EXISTS ext_cine_tab2 AS SELECT 42 AS y"
 extension script file "test_ext_cine--1.0.sql", near line 25
 DROP TABLE ext_cine_tab2;
 CREATE EXTENSION test_ext_cine;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
@@ -475,6 +515,11 @@ Objects in extension "test_ext_cine"
 (14 rows)
 
 ALTER EXTENSION test_ext_cine UPDATE TO '1.1';
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 71f6a0681d..d506c615da 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -565,6 +565,10 @@ CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 ERROR:  relation "mvtest_mv_foo" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELE...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW mvtest_mv_foo.
 NOTICE:  relation "mvtest_mv_foo" already exists, skipping
 CREATE UNIQUE INDEX ON mvtest_mv_foo (i);
 RESET ROLE;
@@ -662,12 +666,20 @@ CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 CREATE MATERIALIZED VIEW matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW matview_ine_tab AS
@@ -676,6 +688,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
@@ -688,6 +704,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
-- 
2.48.0

From 68c8209174f48479df34f37b9ad303a737571473 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Fri, 26 Jul 2024 23:33:15 +0200
Subject: [PATCH v5 3/3] Replace matview WITH OLD DATA

---
 .../sgml/ref/create_materialized_view.sgml    | 16 +++++++++--
 src/backend/commands/createas.c               | 26 +++++++++++------
 src/backend/parser/gram.y                     | 16 +++++++++++
 src/include/nodes/primnodes.h                 |  1 +
 src/test/regress/expected/matview.out         | 28 +++++++++++++++++++
 src/test/regress/sql/matview.sql              | 15 ++++++++++
 6 files changed, 90 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 5e03320eb7..1352e9de40 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -27,7 +27,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     AS <replaceable>query</replaceable>
-    [ WITH [ NO ] DATA ]
+    [ WITH [ NO | OLD ] DATA ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -37,7 +37,8 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
   <para>
    <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
    a query.  The query is executed and used to populate the view at the time
-   the command is issued (unless <command>WITH NO DATA</command> is used) and may be
+   the command is issued (unless <command>WITH NO DATA</command> or
+   <command>WITH OLD DATA</command> is used) and may be
    refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
   </para>
 
@@ -162,7 +163,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
    </varlistentry>
 
    <varlistentry>
-    <term><literal>WITH [ NO ] DATA</literal></term>
+    <term><literal>WITH [ NO | OLD ] DATA</literal></term>
     <listitem>
      <para>
       This clause specifies whether or not the materialized view should be
@@ -170,6 +171,15 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
       flagged as unscannable and cannot be queried until <command>REFRESH
       MATERIALIZED VIEW</command> is used.
      </para>
+
+     <para>
+      The form <command>WITH OLD DATA</command> keeps the already stored data
+      when replacing an existing materialized view to keep it populated.  For
+      newly created materialized views, this has the same effect as
+      <command>WITH DATA</command>.  Use this form if you want to use
+      <command>REFRESH MATERIALIZED VIEW CONCURRENTLY</command> as it requires
+      a populated materialized view.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index cba369114b..1af714fe4a 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -332,18 +332,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* An existing materialized view can be replaced. */
 		if (is_matview && into->replace)
 		{
-			RefreshMatViewStmt *refresh;
-
 			/* Change the relation to match the new query and other options. */
-			(void) create_ctas_nodata(query->targetList, into);
+			address = create_ctas_nodata(query->targetList, into);
 
-			/* Refresh the materialized view with a fake statement. */
-			refresh = makeNode(RefreshMatViewStmt);
-			refresh->relation = into->rel;
-			refresh->skipData = into->skipData;
-			refresh->concurrent = false;
+			/*
+			 * Refresh the materialized view with a fake statement unless we
+			 * must keep the old data.
+			 */
+			if (!into->keepData)
+			{
+				RefreshMatViewStmt *refresh;
+
+				refresh = makeNode(RefreshMatViewStmt);
+				refresh->relation = into->rel;
+				refresh->skipData = into->skipData;
+				refresh->concurrent = false;
+
+				address = ExecRefreshMatView(refresh, NULL, NULL);
+			}
 
-			return ExecRefreshMatView(refresh, NULL, NULL);
+			return address;
 		}
 
 		return InvalidObjectAddress;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index cb5647dcb6..9e7041f98e 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4883,6 +4883,22 @@ CreateMatViewStmt:
 					$7->replace = true;
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt WITH OLD DATA_P
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = false;
+					$7->keepData = true;
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index fce057a8ac..793c971133 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -168,6 +168,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		keepData;		/* true for WITH OLD DATA */
 	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index d506c615da..04c2095c74 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -751,6 +751,23 @@ SELECT * FROM mvtest_replace;
  3
 (1 row)
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 5
+(1 row)
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -905,3 +922,14 @@ ERROR:  syntax error at or near "NOT"
 LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
                                                ^
 DROP MATERIALIZED VIEW mvtest_replace;
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a  
+----
+ 17
+(1 row)
+
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index d6a4dc4b85..91f547e9cb 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -338,6 +338,14 @@ SELECT * FROM mvtest_replace; -- error: not populated
 REFRESH MATERIALIZED VIEW mvtest_replace;
 SELECT * FROM mvtest_replace;
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -422,3 +430,10 @@ CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
   SELECT 1 AS a;
 
 DROP MATERIALIZED VIEW mvtest_replace;
+
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
-- 
2.48.0

From 6ec126d8da5ca80f93ea8a58e07d654f5e21ef6d Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 21 May 2024 18:35:47 +0200
Subject: [PATCH v6 1/3] Add CREATE OR REPLACE MATERIALIZED VIEW

---
 .../sgml/ref/create_materialized_view.sgml    |  15 +-
 src/backend/commands/createas.c               | 207 ++++++++++++++----
 src/backend/commands/tablecmds.c              |   8 +-
 src/backend/commands/view.c                   | 106 ++++++---
 src/backend/parser/gram.y                     |  15 ++
 src/bin/psql/tab-complete.in.c                |  26 ++-
 src/include/commands/view.h                   |   3 +
 src/include/nodes/parsenodes.h                |   2 +-
 src/include/nodes/primnodes.h                 |   1 +
 src/test/regress/expected/matview.out         | 191 ++++++++++++++++
 src/test/regress/sql/matview.sql              | 108 +++++++++
 11 files changed, 589 insertions(+), 93 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 62d897931c3..5e03320eb73 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
+CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ USING <replaceable class="parameter">method</replaceable> ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
@@ -60,6 +60,17 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>OR REPLACE</literal></term>
+    <listitem>
+     <para>
+      Replaces a materialized view if it already exists.
+      Specifying <literal>OR REPLACE</literal> together with
+      <literal>IF NOT EXISTS</literal> is an error.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
@@ -67,7 +78,7 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
       Do not throw an error if a materialized view with the same name already
       exists. A notice is issued in this case.  Note that there is no guarantee
       that the existing materialized view is anything like the one that would
-      have been created.
+      have been created, unless you use <literal>OR REPLACE</literal> instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 44b4665ccd3..9f37ed7f177 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -79,55 +79,151 @@ static void intorel_destroy(DestReceiver *self);
 static ObjectAddress
 create_ctas_internal(List *attrList, IntoClause *into)
 {
-	CreateStmt *create = makeNode(CreateStmt);
-	bool		is_matview;
+	bool		is_matview,
+				replace = false;
 	char		relkind;
-	Datum		toast_options;
-	const char *const validnsps[] = HEAP_RELOPT_NAMESPACES;
+	Oid			matviewOid = InvalidOid;
 	ObjectAddress intoRelationAddr;
 
 	/* This code supports both CREATE TABLE AS and CREATE MATERIALIZED VIEW */
 	is_matview = (into->viewQuery != NULL);
 	relkind = is_matview ? RELKIND_MATVIEW : RELKIND_RELATION;
 
-	/*
-	 * Create the target relation by faking up a CREATE TABLE parsetree and
-	 * passing it to DefineRelation.
-	 */
-	create->relation = into->rel;
-	create->tableElts = attrList;
-	create->inhRelations = NIL;
-	create->ofTypename = NULL;
-	create->constraints = NIL;
-	create->options = into->options;
-	create->oncommit = into->onCommit;
-	create->tablespacename = into->tableSpaceName;
-	create->if_not_exists = false;
-	create->accessMethod = into->accessMethod;
+	/* Check if an existing materialized view needs to be replaced. */
+	if (is_matview)
+	{
+		LOCKMODE	lockmode;
 
-	/*
-	 * Create the relation.  (This will error out if there's an existing view,
-	 * so we don't need more code to complain if "replace" is false.)
-	 */
-	intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL, NULL);
+		lockmode = into->replace ? AccessExclusiveLock : NoLock;
+		(void) RangeVarGetAndCheckCreationNamespace(into->rel, lockmode,
+													&matviewOid);
+		replace = OidIsValid(matviewOid) && into->replace;
+	}
 
-	/*
-	 * If necessary, create a TOAST table for the target table.  Note that
-	 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
-	 * that the TOAST table will be visible for insertion.
-	 */
-	CommandCounterIncrement();
+	if (is_matview && replace)
+	{
+		Relation	rel;
+		List	   *atcmds = NIL;
+		AlterTableCmd *atcmd;
+		TupleDesc	descriptor;
+
+		rel = relation_open(matviewOid, NoLock);
+
+		if (rel->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					errmsg("\"%s\" is not a materialized view",
+						   RelationGetRelationName(rel)));
+
+		CheckTableNotInUse(rel, "CREATE OR REPLACE MATERIALIZED VIEW");
+
+		descriptor = BuildDescForRelation(attrList);
+		checkViewColumns(descriptor, rel->rd_att, true);
+
+		/* Add new attributes via ALTER TABLE. */
+		if (list_length(attrList) > rel->rd_att->natts)
+		{
+			ListCell   *c;
+			int			skip = rel->rd_att->natts;
+
+			foreach(c, attrList)
+			{
+				if (skip > 0)
+				{
+					skip--;
+					continue;
+				}
+				atcmd = makeNode(AlterTableCmd);
+				atcmd->subtype = AT_AddColumnToView;
+				atcmd->def = (Node *) lfirst(c);
+				atcmds = lappend(atcmds, atcmd);
+			}
+		}
+
+		/* Set access method via ALTER TABLE. */
+		if (into->accessMethod != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetAccessMethod;
+			atcmd->name = into->accessMethod;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set tablespace via ALTER TABLE. */
+		if (into->tableSpaceName != NULL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_SetTableSpace;
+			atcmd->name = into->tableSpaceName;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		/* Set storage parameters via ALTER TABLE. */
+		if (into->options != NIL)
+		{
+			atcmd = makeNode(AlterTableCmd);
+			atcmd->subtype = AT_ReplaceRelOptions;
+			atcmd->def = (Node *) into->options;
+			atcmds = lappend(atcmds, atcmd);
+		}
+
+		if (atcmds != NIL)
+		{
+			AlterTableInternal(matviewOid, atcmds, true);
+			CommandCounterIncrement();
+		}
+
+		relation_close(rel, NoLock);
+
+		ObjectAddressSet(intoRelationAddr, RelationRelationId, matviewOid);
+	}
+	else
+	{
+		CreateStmt *create = makeNode(CreateStmt);
+		Datum		toast_options;
+		const static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+
+		/*
+		 * Create the target relation by faking up a CREATE TABLE parsetree
+		 * and passing it to DefineRelation.
+		 */
+		create->relation = into->rel;
+		create->tableElts = attrList;
+		create->inhRelations = NIL;
+		create->ofTypename = NULL;
+		create->constraints = NIL;
+		create->options = into->options;
+		create->oncommit = into->onCommit;
+		create->tablespacename = into->tableSpaceName;
+		create->if_not_exists = false;
+		create->accessMethod = into->accessMethod;
+
+		/*
+		 * Create the relation.  (This will error out if there's an existing
+		 * view, so we don't need more code to complain if "replace" is
+		 * false.)
+		 */
+		intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL,
+										  NULL);
 
-	/* parse and validate reloptions for the toast table */
-	toast_options = transformRelOptions((Datum) 0,
-										create->options,
-										"toast",
-										validnsps,
-										true, false);
+		/*
+		 * If necessary, create a TOAST table for the target table.  Note that
+		 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
+		 * that the TOAST table will be visible for insertion.
+		 */
+		CommandCounterIncrement();
+
+		/* parse and validate reloptions for the toast table */
+		toast_options = transformRelOptions((Datum) 0,
+											create->options,
+											"toast",
+											validnsps,
+											true, false);
 
-	(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
+		(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
 
-	NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+		NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+	}
 
 	/* Create the "view" part of a materialized view. */
 	if (is_matview)
@@ -135,7 +231,7 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* StoreViewQuery scribbles on tree, so make a copy */
 		Query	   *query = copyObject(into->viewQuery);
 
-		StoreViewQuery(intoRelationAddr.objectId, query, false);
+		StoreViewQuery(intoRelationAddr.objectId, query, replace);
 		CommandCounterIncrement();
 	}
 
@@ -232,7 +328,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 
 	/* Check if the relation exists or not */
 	if (CreateTableAsRelExists(stmt))
+	{
+		/* An existing materialized view can be replaced. */
+		if (is_matview && into->replace)
+		{
+			RefreshMatViewStmt *refresh;
+
+			/* Change the relation to match the new query and other options. */
+			(void) create_ctas_nodata(query->targetList, into);
+
+			/* Refresh the materialized view with a fake statement. */
+			refresh = makeNode(RefreshMatViewStmt);
+			refresh->relation = into->rel;
+			refresh->skipData = into->skipData;
+			refresh->concurrent = false;
+
+			return ExecRefreshMatView(refresh, pstate->p_sourcetext, qc);
+		}
+
 		return InvalidObjectAddress;
+	}
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -401,14 +516,15 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 	oldrelid = get_relname_relid(into->rel->relname, nspid);
 	if (OidIsValid(oldrelid))
 	{
-		if (!ctas->if_not_exists)
+		if (!ctas->if_not_exists && !into->replace)
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_TABLE),
 					 errmsg("relation \"%s\" already exists",
 							into->rel->relname)));
 
 		/*
-		 * The relation exists and IF NOT EXISTS has been specified.
+		 * The relation exists and IF NOT EXISTS or OR REPLACE has been
+		 * specified.
 		 *
 		 * If we are in an extension script, insist that the pre-existing
 		 * object be a member of the extension, to avoid security risks.
@@ -416,11 +532,12 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 		ObjectAddressSet(address, RelationRelationId, oldrelid);
 		checkMembershipInCurrentExtension(&address);
 
-		/* OK to skip */
-		ereport(NOTICE,
-				(errcode(ERRCODE_DUPLICATE_TABLE),
-				 errmsg("relation \"%s\" already exists, skipping",
-						into->rel->relname)));
+		if (ctas->if_not_exists)
+			/* OK to skip */
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							into->rel->relname)));
 		return true;
 	}
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 59156a1c1f6..49713bc0422 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4605,7 +4605,7 @@ AlterTableGetLockLevel(List *cmds)
 				 * Subcommands that may be visible to concurrent SELECTs
 				 */
 			case AT_DropColumn: /* change visible to SELECT */
-			case AT_AddColumnToView:	/* CREATE VIEW */
+			case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			case AT_DropOids:	/* used to equiv to DropColumn */
 			case AT_EnableAlwaysRule:	/* may change SELECT rules */
 			case AT_EnableReplicaRule:	/* may change SELECT rules */
@@ -4900,8 +4900,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
-			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW);
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
+			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW | ATT_MATVIEW);
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, true, cmd,
 							lockmode, context);
 			/* Recursion occurs during execution phase */
@@ -5332,7 +5332,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 	switch (cmd->subtype)
 	{
 		case AT_AddColumn:		/* ADD COLUMN */
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			address = ATExecAddColumn(wqueue, tab, rel, &cmd,
 									  cmd->recurse, false,
 									  lockmode, cur_pass, context);
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index 6f0301555e0..53d4cacc4c1 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -30,8 +30,6 @@
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 
-static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
-
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -129,7 +127,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		 * column list.
 		 */
 		descriptor = BuildDescForRelation(attrList);
-		checkViewColumns(descriptor, rel->rd_att);
+		checkViewColumns(descriptor, rel->rd_att, false);
 
 		/*
 		 * If new attributes have been added, we must add pg_attribute entries
@@ -263,15 +261,22 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
  * added to generate specific complaints.  Also, we allow the new view to have
  * more columns than the old.
  */
-static void
-checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
+void
+checkViewColumns(TupleDesc newdesc, TupleDesc olddesc, bool is_matview)
 {
 	int			i;
 
 	if (newdesc->natts < olddesc->natts)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot drop columns from view")));
+	{
+		if (is_matview)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot drop columns from materialized view"));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot drop columns from view")));
+	}
 
 	for (i = 0; i < olddesc->natts; i++)
 	{
@@ -280,17 +285,34 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 
 		/* XXX msg not right, but we don't support DROP COL on view anyway */
 		if (newattr->attisdropped != oldattr->attisdropped)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot drop columns from view")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot drop columns from materialized view"));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot drop columns from view")));
+		}
 
 		if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							NameStr(newattr->attname)),
-					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change name of materialized view column \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   NameStr(newattr->attname)),
+						errhint("Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead."));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change name of view column \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								NameStr(newattr->attname)),
+						 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		}
 
 		/*
 		 * We cannot allow type, typmod, or collation to change, since these
@@ -299,26 +321,48 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 		 */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change data type of view column \"%s\" from %s to %s",
-							NameStr(oldattr->attname),
-							format_type_with_typemod(oldattr->atttypid,
-													 oldattr->atttypmod),
-							format_type_with_typemod(newattr->atttypid,
-													 newattr->atttypmod))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change data type of materialized view column \"%s\" from %s to %s",
+							   NameStr(oldattr->attname),
+							   format_type_with_typemod(oldattr->atttypid,
+														oldattr->atttypmod),
+							   format_type_with_typemod(newattr->atttypid,
+														newattr->atttypmod)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change data type of view column \"%s\" from %s to %s",
+								NameStr(oldattr->attname),
+								format_type_with_typemod(oldattr->atttypid,
+														 oldattr->atttypmod),
+								format_type_with_typemod(newattr->atttypid,
+														 newattr->atttypmod))));
+		}
 
 		/*
 		 * At this point, attcollations should be both valid or both invalid,
 		 * so applying get_collation_name unconditionally should be fine.
 		 */
 		if (newattr->attcollation != oldattr->attcollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							get_collation_name(oldattr->attcollation),
-							get_collation_name(newattr->attcollation))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change collation of materialized view column \"%s\" from \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   get_collation_name(oldattr->attcollation),
+							   get_collation_name(newattr->attcollation)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								get_collation_name(oldattr->attcollation),
+								get_collation_name(newattr->attcollation))));
+		}
 	}
 
 	/*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 271ae26cbaf..d2edc460378 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4895,6 +4895,21 @@ CreateMatViewStmt:
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = !($10);
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 8432be641ac..e862b135a73 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -2162,7 +2162,7 @@ match_previous_words(int pattern_id,
 	/* complete with something you can create or replace */
 	else if (TailMatches("CREATE", "OR", "REPLACE"))
 		COMPLETE_WITH("FUNCTION", "PROCEDURE", "LANGUAGE", "RULE", "VIEW",
-					  "AGGREGATE", "TRANSFORM", "TRIGGER");
+					  "AGGREGATE", "TRANSFORM", "TRIGGER", "MATERIALIZED VIEW");
 
 /* DROP, but not DROP embedded in other commands */
 	/* complete with something you can drop */
@@ -4008,28 +4008,34 @@ match_previous_words(int pattern_id,
 		COMPLETE_WITH("SELECT");
 
 /* CREATE MATERIALIZED VIEW */
-	else if (Matches("CREATE", "MATERIALIZED"))
+	else if (Matches("CREATE", "MATERIALIZED") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED"))
 		COMPLETE_WITH("VIEW");
-	/* Complete CREATE MATERIALIZED VIEW <name> with AS or USING */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> with AS or USING */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("AS", "USING");
 
 	/*
-	 * Complete CREATE MATERIALIZED VIEW <name> USING with list of access
+	 * Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> USING with list of access
 	 * methods
 	 */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING"))
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_table_access_methods);
-	/* Complete CREATE MATERIALIZED VIEW <name> USING <access method> with AS */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> USING <access method> with AS */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny))
 		COMPLETE_WITH("AS");
 
 	/*
-	 * Complete CREATE MATERIALIZED VIEW <name> [USING <access method> ] AS
+	 * Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> [USING <access method> ] AS
 	 * with "SELECT"
 	 */
 	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
-			 Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS"))
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
+			 Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS"))
 		COMPLETE_WITH("SELECT");
 
 /* CREATE EVENT TRIGGER */
diff --git a/src/include/commands/view.h b/src/include/commands/view.h
index c41f51b161c..95290f0a1c4 100644
--- a/src/include/commands/view.h
+++ b/src/include/commands/view.h
@@ -22,4 +22,7 @@ extern ObjectAddress DefineView(ViewStmt *stmt, const char *queryString,
 
 extern void StoreViewQuery(Oid viewOid, Query *viewParse, bool replace);
 
+extern void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc,
+							 bool is_matview);
+
 #endif							/* VIEW_H */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 23c9e3c5abf..5a25ba96ab3 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2402,7 +2402,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
-	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
+	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE [MATERIALIZED] VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_CookedColumnDefault,		/* add a pre-cooked column default */
 	AT_DropNotNull,				/* alter column drop not null */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index d0576da3e25..e800d13a6e0 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -169,6 +169,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 54939ecc6b0..c0cf8ecbffc 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -694,3 +694,194 @@ NOTICE:  relation "matview_ine_tab" already exists, skipping
 (0 rows)
 
 DROP MATERIALIZED VIEW matview_ine_tab;
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+NOTICE:  materialized view "mvtest_replace" does not exist, skipping
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 1
+(1 row)
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 2
+(1 row)
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+ERROR:  materialized view "mvtest_replace" has not been populated
+HINT:  Use the REFRESH MATERIALIZED VIEW command.
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 4 | 1
+(1 row)
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 4 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     |   reloptions    |     spcname      | amname 
+---+---+----------------+-----------------+------------------+--------
+ 5 | 1 | mvtest_replace | {fillfactor=50} | regress_tblspace | heap2
+(1 row)
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+ a | b | a | b 
+---+---+---+---
+ 6 | 1 | 6 | 1
+(1 row)
+
+DROP VIEW mvtest_replace_v;
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+RESET enable_seqscan;
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+ERROR:  cannot change data type of materialized view column "b" from integer to text
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+ERROR:  cannot change name of materialized view column "b" to "b2"
+HINT:  Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead.
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+ERROR:  cannot change collation of materialized view column "c" from "C" to "POSIX"
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+ERROR:  cannot drop columns from materialized view
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+ERROR:  "mvtest_not_mv" is not a materialized view
+DROP VIEW mvtest_not_mv;
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+ERROR:  syntax error at or near "NOT"
+LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
+                                               ^
+DROP MATERIALIZED VIEW mvtest_replace;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index 6704eeae2df..d6a4dc4b857 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -314,3 +314,111 @@ EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
 DROP MATERIALIZED VIEW matview_ine_tab;
+
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+DROP VIEW mvtest_replace_v;
+
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+SELECT * FROM mvtest_replace;
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+DROP VIEW mvtest_not_mv;
+
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+
+DROP MATERIALIZED VIEW mvtest_replace;
-- 
2.48.1

From 232b1439f6cb5d931540901b8e582bd4e6551abf Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 28 May 2024 02:19:53 +0200
Subject: [PATCH v6 2/3] Deprecate CREATE MATERIALIZED VIEW IF NOT EXISTS

---
 src/backend/parser/gram.y                     | 14 ++++++
 .../expected/test_extensions.out              | 45 +++++++++++++++++++
 src/test/regress/expected/matview.out         | 20 +++++++++
 3 files changed, 79 insertions(+)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index d2edc460378..8be790eaccf 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4894,6 +4894,20 @@ CreateMatViewStmt:
 					$8->rel->relpersistence = $2;
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
+
+					if (ctas->into->rel->schemaname)
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.%s.",
+											ctas->into->rel->schemaname,
+											ctas->into->rel->relname),
+									parser_errposition(@1));
+					else
+							ereport(WARNING,
+									errmsg("IF NOT EXISTS is deprecated in materialized view creation"),
+									errhint("Use CREATE OR REPLACE MATERIALIZED VIEW %s.",
+											ctas->into->rel->relname),
+									parser_errposition(@1));
 				}
 		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
 				{
diff --git a/src/test/modules/test_extensions/expected/test_extensions.out b/src/test/modules/test_extensions/expected/test_extensions.out
index d5388a1fecf..9a1e0f76587 100644
--- a/src/test/modules/test_extensions/expected/test_extensions.out
+++ b/src/test/modules/test_extensions/expected/test_extensions.out
@@ -404,6 +404,11 @@ Objects in extension "test_ext_cor"
 CREATE COLLATION ext_cine_coll
   ( LC_COLLATE = "C", LC_CTYPE = "C" );
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  collation ext_cine_coll is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE COLLATION IF NOT EXISTS ext_cine_coll
@@ -412,6 +417,11 @@ extension script file "test_ext_cine--1.0.sql", near line 10
 DROP COLLATION ext_cine_coll;
 CREATE MATERIALIZED VIEW ext_cine_mv AS SELECT 11 AS f1;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  materialized view ext_cine_mv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1"
@@ -420,6 +430,11 @@ DROP MATERIALIZED VIEW ext_cine_mv;
 CREATE FOREIGN DATA WRAPPER dummy;
 CREATE SERVER ext_cine_srv FOREIGN DATA WRAPPER dummy;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  server ext_cine_srv is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SERVER IF NOT EXISTS ext_cine_srv FOREIGN DATA WRAPPER ext_cine_fdw"
@@ -427,6 +442,11 @@ extension script file "test_ext_cine--1.0.sql", near line 17
 DROP SERVER ext_cine_srv;
 CREATE SCHEMA ext_cine_schema;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  schema ext_cine_schema is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SCHEMA IF NOT EXISTS ext_cine_schema"
@@ -434,6 +454,11 @@ extension script file "test_ext_cine--1.0.sql", near line 19
 DROP SCHEMA ext_cine_schema;
 CREATE SEQUENCE ext_cine_seq;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  sequence ext_cine_seq is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE SEQUENCE IF NOT EXISTS ext_cine_seq"
@@ -441,6 +466,11 @@ extension script file "test_ext_cine--1.0.sql", near line 21
 DROP SEQUENCE ext_cine_seq;
 CREATE TABLE ext_cine_tab1 (x int);
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  table ext_cine_tab1 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE TABLE IF NOT EXISTS ext_cine_tab1 (x int)"
@@ -448,12 +478,22 @@ extension script file "test_ext_cine--1.0.sql", near line 23
 DROP TABLE ext_cine_tab1;
 CREATE TABLE ext_cine_tab2 AS SELECT 42 AS y;
 CREATE EXTENSION test_ext_cine;  -- fail
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 ERROR:  table ext_cine_tab2 is not a member of extension "test_ext_cine"
 DETAIL:  An extension may only use CREATE ... IF NOT EXISTS to skip object creation if the conflicting object is one that it already owns.
 CONTEXT:  SQL statement "CREATE TABLE IF NOT EXISTS ext_cine_tab2 AS SELECT 42 AS y"
 extension script file "test_ext_cine--1.0.sql", near line 25
 DROP TABLE ext_cine_tab2;
 CREATE EXTENSION test_ext_cine;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
@@ -475,6 +515,11 @@ Objects in extension "test_ext_cine"
 (14 rows)
 
 ALTER EXTENSION test_ext_cine UPDATE TO '1.1';
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW ext_cine_mv.
+QUERY:  CREATE MATERIALIZED VIEW IF NOT EXISTS ext_cine_mv AS SELECT 42 AS f1;
 \dx+ test_ext_cine
 Objects in extension "test_ext_cine"
         Object description         
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index c0cf8ecbffc..d4b42da1ddf 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -565,6 +565,10 @@ CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 CREATE MATERIALIZED VIEW mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
 ERROR:  relation "mvtest_mv_foo" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELECT * FROM mvtest_foo_data;
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS mvtest_mv_foo AS SELE...
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW mvtest_mv_foo.
 NOTICE:  relation "mvtest_mv_foo" already exists, skipping
 CREATE UNIQUE INDEX ON mvtest_mv_foo (i);
 RESET ROLE;
@@ -662,12 +666,20 @@ CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 CREATE MATERIALIZED VIEW matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- error
 ERROR:  relation "matview_ine_tab" already exists
 CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
   SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 1: CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+        ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW matview_ine_tab AS
@@ -676,6 +688,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
@@ -688,6 +704,10 @@ ERROR:  relation "matview_ine_tab" already exists
 EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
+WARNING:  IF NOT EXISTS is deprecated in materialized view creation
+LINE 2:   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+          ^
+HINT:  Use CREATE OR REPLACE MATERIALIZED VIEW matview_ine_tab.
 NOTICE:  relation "matview_ine_tab" already exists, skipping
  QUERY PLAN 
 ------------
-- 
2.48.1

From eba3f5904ff97217a07628948fd3c707f5d9e94d Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Fri, 26 Jul 2024 23:33:15 +0200
Subject: [PATCH v6 3/3] Replace matview WITH OLD DATA

---
 .../sgml/ref/create_materialized_view.sgml    | 16 +++++++++--
 src/backend/commands/createas.c               | 26 +++++++++++------
 src/backend/parser/gram.y                     | 16 +++++++++++
 src/include/nodes/primnodes.h                 |  1 +
 src/test/regress/expected/matview.out         | 28 +++++++++++++++++++
 src/test/regress/sql/matview.sql              | 15 ++++++++++
 6 files changed, 90 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 5e03320eb73..1352e9de409 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -27,7 +27,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     AS <replaceable>query</replaceable>
-    [ WITH [ NO ] DATA ]
+    [ WITH [ NO | OLD ] DATA ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -37,7 +37,8 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
   <para>
    <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
    a query.  The query is executed and used to populate the view at the time
-   the command is issued (unless <command>WITH NO DATA</command> is used) and may be
+   the command is issued (unless <command>WITH NO DATA</command> or
+   <command>WITH OLD DATA</command> is used) and may be
    refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
   </para>
 
@@ -162,7 +163,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
    </varlistentry>
 
    <varlistentry>
-    <term><literal>WITH [ NO ] DATA</literal></term>
+    <term><literal>WITH [ NO | OLD ] DATA</literal></term>
     <listitem>
      <para>
       This clause specifies whether or not the materialized view should be
@@ -170,6 +171,15 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
       flagged as unscannable and cannot be queried until <command>REFRESH
       MATERIALIZED VIEW</command> is used.
      </para>
+
+     <para>
+      The form <command>WITH OLD DATA</command> keeps the already stored data
+      when replacing an existing materialized view to keep it populated.  For
+      newly created materialized views, this has the same effect as
+      <command>WITH DATA</command>.  Use this form if you want to use
+      <command>REFRESH MATERIALIZED VIEW CONCURRENTLY</command> as it requires
+      a populated materialized view.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 9f37ed7f177..0ed44b246bd 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -332,18 +332,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* An existing materialized view can be replaced. */
 		if (is_matview && into->replace)
 		{
-			RefreshMatViewStmt *refresh;
-
 			/* Change the relation to match the new query and other options. */
-			(void) create_ctas_nodata(query->targetList, into);
+			address = create_ctas_nodata(query->targetList, into);
 
-			/* Refresh the materialized view with a fake statement. */
-			refresh = makeNode(RefreshMatViewStmt);
-			refresh->relation = into->rel;
-			refresh->skipData = into->skipData;
-			refresh->concurrent = false;
+			/*
+			 * Refresh the materialized view with a fake statement unless we
+			 * must keep the old data.
+			 */
+			if (!into->keepData)
+			{
+				RefreshMatViewStmt *refresh;
+
+				refresh = makeNode(RefreshMatViewStmt);
+				refresh->relation = into->rel;
+				refresh->skipData = into->skipData;
+				refresh->concurrent = false;
+
+				address = ExecRefreshMatView(refresh, pstate->p_sourcetext, qc);
+			}
 
-			return ExecRefreshMatView(refresh, pstate->p_sourcetext, qc);
+			return address;
 		}
 
 		return InvalidObjectAddress;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 8be790eaccf..e405268f413 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4924,6 +4924,22 @@ CreateMatViewStmt:
 					$7->replace = true;
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt WITH OLD DATA_P
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = false;
+					$7->keepData = true;
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index e800d13a6e0..5290e6c0e8a 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -169,6 +169,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		keepData;		/* true for WITH OLD DATA */
 	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index d4b42da1ddf..f0f52dd1c6c 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -751,6 +751,23 @@ SELECT * FROM mvtest_replace;
  3
 (1 row)
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 5
+(1 row)
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -905,3 +922,14 @@ ERROR:  syntax error at or near "NOT"
 LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
                                                ^
 DROP MATERIALIZED VIEW mvtest_replace;
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a  
+----
+ 17
+(1 row)
+
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index d6a4dc4b857..91f547e9cb8 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -338,6 +338,14 @@ SELECT * FROM mvtest_replace; -- error: not populated
 REFRESH MATERIALIZED VIEW mvtest_replace;
 SELECT * FROM mvtest_replace;
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -422,3 +430,10 @@ CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
   SELECT 1 AS a;
 
 DROP MATERIALIZED VIEW mvtest_replace;
+
+-- Create new matview WITH OLD DATA.  This populates the new matview as if
+-- WITH DATA had been specified.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
-- 
2.48.1

From 8fff179bf323ca8b4a96b977ab3193db483114cd Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 21 May 2024 18:35:47 +0200
Subject: [PATCH v7 1/3] Add OR REPLACE option to CREATE MATERIALIZED VIEW

---
 .../sgml/ref/create_materialized_view.sgml    |  15 +-
 src/backend/commands/createas.c               | 219 ++++++++++++++----
 src/backend/commands/tablecmds.c              |   8 +-
 src/backend/commands/view.c                   | 106 ++++++---
 src/backend/parser/gram.y                     |  15 ++
 src/bin/psql/tab-complete.in.c                |  26 ++-
 src/include/commands/view.h                   |   3 +
 src/include/nodes/parsenodes.h                |   2 +-
 src/include/nodes/primnodes.h                 |   1 +
 src/test/regress/expected/matview.out         | 205 ++++++++++++++++
 src/test/regress/sql/matview.sql              | 117 ++++++++++
 11 files changed, 624 insertions(+), 93 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 62d897931c3..5e03320eb73 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
+CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
     [ (<replaceable>column_name</replaceable> [, ...] ) ]
     [ USING <replaceable class="parameter">method</replaceable> ]
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
@@ -60,6 +60,17 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>OR REPLACE</literal></term>
+    <listitem>
+     <para>
+      Replaces a materialized view if it already exists.
+      Specifying <literal>OR REPLACE</literal> together with
+      <literal>IF NOT EXISTS</literal> is an error.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF NOT EXISTS</literal></term>
     <listitem>
@@ -67,7 +78,7 @@ CREATE MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_name</replaceable>
       Do not throw an error if a materialized view with the same name already
       exists. A notice is issued in this case.  Note that there is no guarantee
       that the existing materialized view is anything like the one that would
-      have been created.
+      have been created, unless you use <literal>OR REPLACE</literal> instead.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index dfd2ab8e862..1620273f965 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -24,6 +24,7 @@
  */
 #include "postgres.h"
 
+#include "miscadmin.h"
 #include "access/heapam.h"
 #include "access/reloptions.h"
 #include "access/tableam.h"
@@ -34,6 +35,7 @@
 #include "commands/matview.h"
 #include "commands/prepare.h"
 #include "commands/tablecmds.h"
+#include "commands/tablespace.h"
 #include "commands/view.h"
 #include "executor/execdesc.h"
 #include "executor/executor.h"
@@ -81,55 +83,161 @@ static void intorel_destroy(DestReceiver *self);
 static ObjectAddress
 create_ctas_internal(List *attrList, IntoClause *into)
 {
-	CreateStmt *create = makeNode(CreateStmt);
-	bool		is_matview;
+	bool		is_matview,
+				replace = false;
 	char		relkind;
-	Datum		toast_options;
-	const char *const validnsps[] = HEAP_RELOPT_NAMESPACES;
+	Oid			matviewOid = InvalidOid;
 	ObjectAddress intoRelationAddr;
 
 	/* This code supports both CREATE TABLE AS and CREATE MATERIALIZED VIEW */
 	is_matview = (into->viewQuery != NULL);
 	relkind = is_matview ? RELKIND_MATVIEW : RELKIND_RELATION;
 
-	/*
-	 * Create the target relation by faking up a CREATE TABLE parsetree and
-	 * passing it to DefineRelation.
-	 */
-	create->relation = into->rel;
-	create->tableElts = attrList;
-	create->inhRelations = NIL;
-	create->ofTypename = NULL;
-	create->constraints = NIL;
-	create->options = into->options;
-	create->oncommit = into->onCommit;
-	create->tablespacename = into->tableSpaceName;
-	create->if_not_exists = false;
-	create->accessMethod = into->accessMethod;
+	/* Check if an existing materialized view needs to be replaced. */
+	if (is_matview)
+	{
+		LOCKMODE	lockmode;
 
-	/*
-	 * Create the relation.  (This will error out if there's an existing view,
-	 * so we don't need more code to complain if "replace" is false.)
-	 */
-	intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL, NULL);
+		lockmode = into->replace ? AccessExclusiveLock : NoLock;
+		(void) RangeVarGetAndCheckCreationNamespace(into->rel, lockmode,
+													&matviewOid);
+		replace = OidIsValid(matviewOid) && into->replace;
+	}
 
-	/*
-	 * If necessary, create a TOAST table for the target table.  Note that
-	 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
-	 * that the TOAST table will be visible for insertion.
-	 */
-	CommandCounterIncrement();
+	if (is_matview && replace)
+	{
+		Relation	rel;
+		List	   *atcmds = NIL;
+		AlterTableCmd *atcmd;
+		TupleDesc	descriptor;
+
+		rel = relation_open(matviewOid, NoLock);
+
+		if (rel->rd_rel->relkind != RELKIND_MATVIEW)
+			ereport(ERROR,
+					errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					errmsg("\"%s\" is not a materialized view",
+						   RelationGetRelationName(rel)));
+
+		CheckTableNotInUse(rel, "CREATE OR REPLACE MATERIALIZED VIEW");
+
+		descriptor = BuildDescForRelation(attrList);
+		checkViewColumns(descriptor, rel->rd_att, true);
+
+		/* add new attributes */
+		if (list_length(attrList) > rel->rd_att->natts)
+		{
+			ListCell   *c;
+			int			skip = rel->rd_att->natts;
+
+			foreach(c, attrList)
+			{
+				if (skip > 0)
+				{
+					skip--;
+					continue;
+				}
+				atcmd = makeNode(AlterTableCmd);
+				atcmd->subtype = AT_AddColumnToView;
+				atcmd->def = (Node *) lfirst(c);
+				atcmds = lappend(atcmds, atcmd);
+			}
+		}
+
+		/*
+		 * The following alters access method, tablespace, and storage options.
+		 * When replacing an existing matview we need to alter the relation
+		 * such that the defaults apply as if they have not been specified at
+		 * all by the CREATE statement.
+		 */
+
+		/* access method */
+		atcmd = makeNode(AlterTableCmd);
+		atcmd->subtype = AT_SetAccessMethod;
+		atcmd->name = into->accessMethod ? into->accessMethod : default_table_access_method;
+		atcmds = lappend(atcmds, atcmd);
+
+		/* tablespace */
+		atcmd = makeNode(AlterTableCmd);
+		atcmd->subtype = AT_SetTableSpace;
+		if (into->tableSpaceName != NULL)
+			atcmd->name = into->tableSpaceName;
+		else
+		{
+			Oid spcid;
+
+			/*
+			 * Resolve the name of the default or database tablespace because
+			 * we need to specify the tablespace by name.
+			 *
+			 * TODO: Move that to ATPrepSetTableSpace? Must allow AlterTableCmd.name to be NULL then.
+			 */
+			spcid = GetDefaultTablespace(RELPERSISTENCE_PERMANENT, false);
+			if (!OidIsValid(spcid))
+				spcid = MyDatabaseTableSpace;
+			atcmd->name = get_tablespace_name(spcid);
+		}
+		atcmds = lappend(atcmds, atcmd);
+
+		/* storage options */
+		atcmd = makeNode(AlterTableCmd);
+		atcmd->subtype = AT_ReplaceRelOptions;
+		atcmd->def = (Node *) into->options;
+		atcmds = lappend(atcmds, atcmd);
+
+		AlterTableInternal(matviewOid, atcmds, true);
+		CommandCounterIncrement();
+
+		relation_close(rel, NoLock);
+		ObjectAddressSet(intoRelationAddr, RelationRelationId, matviewOid);
+	}
+	else
+	{
+		CreateStmt *create = makeNode(CreateStmt);
+		Datum		toast_options;
+		const static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
+
+		/*
+		 * Create the target relation by faking up a CREATE TABLE parsetree
+		 * and passing it to DefineRelation.
+		 */
+		create->relation = into->rel;
+		create->tableElts = attrList;
+		create->inhRelations = NIL;
+		create->ofTypename = NULL;
+		create->constraints = NIL;
+		create->options = into->options;
+		create->oncommit = into->onCommit;
+		create->tablespacename = into->tableSpaceName;
+		create->if_not_exists = false;
+		create->accessMethod = into->accessMethod;
+
+		/*
+		 * Create the relation.  (This will error out if there's an existing
+		 * view, so we don't need more code to complain if "replace" is
+		 * false.)
+		 */
+		intoRelationAddr = DefineRelation(create, relkind, InvalidOid, NULL,
+										  NULL);
 
-	/* parse and validate reloptions for the toast table */
-	toast_options = transformRelOptions((Datum) 0,
-										create->options,
-										"toast",
-										validnsps,
-										true, false);
+		/*
+		 * If necessary, create a TOAST table for the target table.  Note that
+		 * NewRelationCreateToastTable ends with CommandCounterIncrement(), so
+		 * that the TOAST table will be visible for insertion.
+		 */
+		CommandCounterIncrement();
+
+		/* parse and validate reloptions for the toast table */
+		toast_options = transformRelOptions((Datum) 0,
+											create->options,
+											"toast",
+											validnsps,
+											true, false);
 
-	(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
+		(void) heap_reloptions(RELKIND_TOASTVALUE, toast_options, true);
 
-	NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+		NewRelationCreateToastTable(intoRelationAddr.objectId, toast_options);
+	}
 
 	/* Create the "view" part of a materialized view. */
 	if (is_matview)
@@ -137,7 +245,7 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* StoreViewQuery scribbles on tree, so make a copy */
 		Query	   *query = copyObject(into->viewQuery);
 
-		StoreViewQuery(intoRelationAddr.objectId, query, false);
+		StoreViewQuery(intoRelationAddr.objectId, query, replace);
 		CommandCounterIncrement();
 	}
 
@@ -234,7 +342,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 
 	/* Check if the relation exists or not */
 	if (CreateTableAsRelExists(stmt))
+	{
+		/* An existing materialized view can be replaced. */
+		if (is_matview && into->replace)
+		{
+			RefreshMatViewStmt *refresh;
+
+			/* Change the relation to match the new query and other options. */
+			(void) create_ctas_nodata(query->targetList, into);
+
+			/* Refresh the materialized view with a fake statement. */
+			refresh = makeNode(RefreshMatViewStmt);
+			refresh->relation = into->rel;
+			refresh->skipData = into->skipData;
+			refresh->concurrent = false;
+
+			return ExecRefreshMatView(refresh, pstate->p_sourcetext, qc);
+		}
+
 		return InvalidObjectAddress;
+	}
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -402,14 +529,15 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 	oldrelid = get_relname_relid(into->rel->relname, nspid);
 	if (OidIsValid(oldrelid))
 	{
-		if (!ctas->if_not_exists)
+		if (!ctas->if_not_exists && !into->replace)
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_TABLE),
 					 errmsg("relation \"%s\" already exists",
 							into->rel->relname)));
 
 		/*
-		 * The relation exists and IF NOT EXISTS has been specified.
+		 * The relation exists and IF NOT EXISTS or OR REPLACE has been
+		 * specified.
 		 *
 		 * If we are in an extension script, insist that the pre-existing
 		 * object be a member of the extension, to avoid security risks.
@@ -417,11 +545,12 @@ CreateTableAsRelExists(CreateTableAsStmt *ctas)
 		ObjectAddressSet(address, RelationRelationId, oldrelid);
 		checkMembershipInCurrentExtension(&address);
 
-		/* OK to skip */
-		ereport(NOTICE,
-				(errcode(ERRCODE_DUPLICATE_TABLE),
-				 errmsg("relation \"%s\" already exists, skipping",
-						into->rel->relname)));
+		if (ctas->if_not_exists)
+			/* OK to skip */
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists, skipping",
+							into->rel->relname)));
 		return true;
 	}
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index cb811520c29..44dcd2c5b0d 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4645,7 +4645,7 @@ AlterTableGetLockLevel(List *cmds)
 				 * Subcommands that may be visible to concurrent SELECTs
 				 */
 			case AT_DropColumn: /* change visible to SELECT */
-			case AT_AddColumnToView:	/* CREATE VIEW */
+			case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			case AT_DropOids:	/* used to equiv to DropColumn */
 			case AT_EnableAlwaysRule:	/* may change SELECT rules */
 			case AT_EnableReplicaRule:	/* may change SELECT rules */
@@ -4940,8 +4940,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
-			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW);
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
+			ATSimplePermissions(cmd->subtype, rel, ATT_VIEW | ATT_MATVIEW);
 			ATPrepAddColumn(wqueue, rel, recurse, recursing, true, cmd,
 							lockmode, context);
 			/* Recursion occurs during execution phase */
@@ -5372,7 +5372,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 	switch (cmd->subtype)
 	{
 		case AT_AddColumn:		/* ADD COLUMN */
-		case AT_AddColumnToView:	/* add column via CREATE OR REPLACE VIEW */
+		case AT_AddColumnToView:	/* via CREATE OR REPLACE [MATERIALIZED] VIEW */
 			address = ATExecAddColumn(wqueue, tab, rel, &cmd,
 									  cmd->recurse, false,
 									  lockmode, cur_pass, context);
diff --git a/src/backend/commands/view.c b/src/backend/commands/view.c
index 6f0301555e0..53d4cacc4c1 100644
--- a/src/backend/commands/view.c
+++ b/src/backend/commands/view.c
@@ -30,8 +30,6 @@
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 
-static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
-
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -129,7 +127,7 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
 		 * column list.
 		 */
 		descriptor = BuildDescForRelation(attrList);
-		checkViewColumns(descriptor, rel->rd_att);
+		checkViewColumns(descriptor, rel->rd_att, false);
 
 		/*
 		 * If new attributes have been added, we must add pg_attribute entries
@@ -263,15 +261,22 @@ DefineVirtualRelation(RangeVar *relation, List *tlist, bool replace,
  * added to generate specific complaints.  Also, we allow the new view to have
  * more columns than the old.
  */
-static void
-checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
+void
+checkViewColumns(TupleDesc newdesc, TupleDesc olddesc, bool is_matview)
 {
 	int			i;
 
 	if (newdesc->natts < olddesc->natts)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot drop columns from view")));
+	{
+		if (is_matview)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot drop columns from materialized view"));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot drop columns from view")));
+	}
 
 	for (i = 0; i < olddesc->natts; i++)
 	{
@@ -280,17 +285,34 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 
 		/* XXX msg not right, but we don't support DROP COL on view anyway */
 		if (newattr->attisdropped != oldattr->attisdropped)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot drop columns from view")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot drop columns from materialized view"));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot drop columns from view")));
+		}
 
 		if (strcmp(NameStr(newattr->attname), NameStr(oldattr->attname)) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							NameStr(newattr->attname)),
-					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change name of materialized view column \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   NameStr(newattr->attname)),
+						errhint("Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead."));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change name of view column \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								NameStr(newattr->attname)),
+						 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
+		}
 
 		/*
 		 * We cannot allow type, typmod, or collation to change, since these
@@ -299,26 +321,48 @@ checkViewColumns(TupleDesc newdesc, TupleDesc olddesc)
 		 */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change data type of view column \"%s\" from %s to %s",
-							NameStr(oldattr->attname),
-							format_type_with_typemod(oldattr->atttypid,
-													 oldattr->atttypmod),
-							format_type_with_typemod(newattr->atttypid,
-													 newattr->atttypmod))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change data type of materialized view column \"%s\" from %s to %s",
+							   NameStr(oldattr->attname),
+							   format_type_with_typemod(oldattr->atttypid,
+														oldattr->atttypmod),
+							   format_type_with_typemod(newattr->atttypid,
+														newattr->atttypmod)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change data type of view column \"%s\" from %s to %s",
+								NameStr(oldattr->attname),
+								format_type_with_typemod(oldattr->atttypid,
+														 oldattr->atttypmod),
+								format_type_with_typemod(newattr->atttypid,
+														 newattr->atttypmod))));
+		}
 
 		/*
 		 * At this point, attcollations should be both valid or both invalid,
 		 * so applying get_collation_name unconditionally should be fine.
 		 */
 		if (newattr->attcollation != oldattr->attcollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-					 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
-							NameStr(oldattr->attname),
-							get_collation_name(oldattr->attcollation),
-							get_collation_name(newattr->attcollation))));
+		{
+			if (is_matview)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot change collation of materialized view column \"%s\" from \"%s\" to \"%s\"",
+							   NameStr(oldattr->attname),
+							   get_collation_name(oldattr->attcollation),
+							   get_collation_name(newattr->attcollation)));
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						 errmsg("cannot change collation of view column \"%s\" from \"%s\" to \"%s\"",
+								NameStr(oldattr->attname),
+								get_collation_name(oldattr->attcollation),
+								get_collation_name(newattr->attcollation))));
+		}
 	}
 
 	/*
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index db43034b9db..7aaf0e37ad8 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4929,6 +4929,21 @@ CreateMatViewStmt:
 					$8->skipData = !($11);
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt opt_with_data
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = !($10);
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 1f2ca946fc5..f49f0b60c95 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -2187,7 +2187,7 @@ match_previous_words(int pattern_id,
 	/* complete with something you can create or replace */
 	else if (TailMatches("CREATE", "OR", "REPLACE"))
 		COMPLETE_WITH("FUNCTION", "PROCEDURE", "LANGUAGE", "RULE", "VIEW",
-					  "AGGREGATE", "TRANSFORM", "TRIGGER");
+					  "AGGREGATE", "TRANSFORM", "TRIGGER", "MATERIALIZED VIEW");
 
 /* DROP, but not DROP embedded in other commands */
 	/* complete with something you can drop */
@@ -4072,28 +4072,34 @@ match_previous_words(int pattern_id,
 		COMPLETE_WITH("SELECT");
 
 /* CREATE MATERIALIZED VIEW */
-	else if (Matches("CREATE", "MATERIALIZED"))
+	else if (Matches("CREATE", "MATERIALIZED") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED"))
 		COMPLETE_WITH("VIEW");
-	/* Complete CREATE MATERIALIZED VIEW <name> with AS or USING */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> with AS or USING */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("AS", "USING");
 
 	/*
-	 * Complete CREATE MATERIALIZED VIEW <name> USING with list of access
+	 * Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> USING with list of access
 	 * methods
 	 */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING"))
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_table_access_methods);
-	/* Complete CREATE MATERIALIZED VIEW <name> USING <access method> with AS */
-	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny))
+	/* Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> USING <access method> with AS */
+	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny) ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny))
 		COMPLETE_WITH("AS");
 
 	/*
-	 * Complete CREATE MATERIALIZED VIEW <name> [USING <access method> ] AS
+	 * Complete CREATE [ OR REPLACE ] MATERIALIZED VIEW <name> [USING <access method> ] AS
 	 * with "SELECT"
 	 */
 	else if (Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
-			 Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS"))
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "AS") ||
+			 Matches("CREATE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS") ||
+			 Matches("CREATE", "OR", "REPLACE", "MATERIALIZED", "VIEW", MatchAny, "USING", MatchAny, "AS"))
 		COMPLETE_WITH("SELECT");
 
 /* CREATE EVENT TRIGGER */
diff --git a/src/include/commands/view.h b/src/include/commands/view.h
index c41f51b161c..95290f0a1c4 100644
--- a/src/include/commands/view.h
+++ b/src/include/commands/view.h
@@ -22,4 +22,7 @@ extern ObjectAddress DefineView(ViewStmt *stmt, const char *queryString,
 
 extern void StoreViewQuery(Oid viewOid, Query *viewParse, bool replace);
 
+extern void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc,
+							 bool is_matview);
+
 #endif							/* VIEW_H */
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 86a236bd58b..74922f8ae89 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2412,7 +2412,7 @@ typedef struct AlterTableStmt
 typedef enum AlterTableType
 {
 	AT_AddColumn,				/* add column */
-	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE VIEW */
+	AT_AddColumnToView,			/* implicitly via CREATE OR REPLACE [MATERIALIZED] VIEW */
 	AT_ColumnDefault,			/* alter column default */
 	AT_CookedColumnDefault,		/* add a pre-cooked column default */
 	AT_DropNotNull,				/* alter column drop not null */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 6dfca3cb35b..3a0c3b06c81 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -169,6 +169,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index c56c9fa3a25..56104b7ee8b 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -694,3 +694,208 @@ NOTICE:  relation "matview_ine_tab" already exists, skipping
 (0 rows)
 
 DROP MATERIALIZED VIEW matview_ine_tab;
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+NOTICE:  materialized view "mvtest_replace" does not exist, skipping
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 1
+(1 row)
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 2
+(1 row)
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+ERROR:  materialized view "mvtest_replace" has not been populated
+HINT:  Use the REFRESH MATERIALIZED VIEW command.
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 4 | 1
+(1 row)
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 4 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     |   reloptions    |     spcname      | amname 
+---+---+----------------+-----------------+------------------+--------
+ 5 | 1 | mvtest_replace | {fillfactor=50} | regress_tblspace | heap2
+(1 row)
+
+-- restore default options
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+ a | b |    relname     | reloptions | spcname | amname 
+---+---+----------------+------------+---------+--------
+ 5 | 1 | mvtest_replace |            |         | heap
+(1 row)
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+ a | b | a | b 
+---+---+---+---
+ 6 | 1 | 6 | 1
+(1 row)
+
+DROP VIEW mvtest_replace_v;
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 7 | 1
+(1 row)
+
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+                       QUERY PLAN                        
+---------------------------------------------------------
+ Index Scan using mvtest_replace_b_idx on mvtest_replace
+   Index Cond: (b = 1)
+(2 rows)
+
+SELECT * FROM mvtest_replace WHERE b = 1;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+RESET enable_seqscan;
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+ERROR:  cannot change data type of materialized view column "b" from integer to text
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+ERROR:  cannot change name of materialized view column "b" to "b2"
+HINT:  Use ALTER MATERIALIZED VIEW ... RENAME COLUMN ... to change name of materialized view column instead.
+SELECT * FROM mvtest_replace;
+ a | b 
+---+---
+ 8 | 1
+(1 row)
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+ERROR:  cannot change collation of materialized view column "c" from "C" to "POSIX"
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+ERROR:  cannot drop columns from materialized view
+SELECT * FROM mvtest_replace;
+ a  | b | c 
+----+---+---
+ 11 | 1 | y
+(1 row)
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+ERROR:  "mvtest_not_mv" is not a materialized view
+DROP VIEW mvtest_not_mv;
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+ERROR:  syntax error at or near "NOT"
+LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
+                                               ^
+DROP MATERIALIZED VIEW mvtest_replace;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index 6704eeae2df..fe0cb4d25bf 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -314,3 +314,120 @@ EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
   CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
     SELECT 1 / 0 WITH NO DATA; -- ok
 DROP MATERIALIZED VIEW matview_ine_tab;
+
+--
+-- test CREATE OR REPLACE MATERIALIZED VIEW
+--
+
+-- matview does not already exist
+DROP MATERIALIZED VIEW IF EXISTS mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 1 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 2 AS a;
+SELECT * FROM mvtest_replace;
+
+-- replace query without data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 3 AS a
+  WITH NO DATA;
+SELECT * FROM mvtest_replace; -- error: not populated
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
+-- add column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 4 AS a, 1 b;
+SELECT * FROM mvtest_replace;
+
+-- replace table options
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  USING heap2
+  WITH (fillfactor = 50)
+  TABLESPACE regress_tblspace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+-- restore default options
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace
+  AS SELECT 5 AS a, 1 AS b;
+SELECT m.*, c.relname, c.reloptions, s.spcname, a.amname
+  FROM mvtest_replace m
+    CROSS JOIN pg_class c
+    LEFT JOIN pg_tablespace s ON s.oid = c.reltablespace
+    LEFT JOIN pg_am a ON a.oid = c.relam
+  WHERE c.relname = 'mvtest_replace';
+
+-- can replace matview that has a dependent view
+CREATE VIEW mvtest_replace_v AS
+  SELECT * FROM mvtest_replace;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 6 AS a, 1 AS b;
+SELECT * FROM mvtest_replace, mvtest_replace_v;
+DROP VIEW mvtest_replace_v;
+
+-- index gets rebuilt when replacing with data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 7 AS a, 1 AS b;
+CREATE UNIQUE INDEX ON mvtest_replace (b);
+SELECT * FROM mvtest_replace;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 8 AS a, 1 AS b;
+SET enable_seqscan = off; -- force index scan
+EXPLAIN (COSTS OFF) SELECT * FROM mvtest_replace WHERE b = 1;
+SELECT * FROM mvtest_replace WHERE b = 1;
+RESET enable_seqscan;
+
+-- cannot change column data type
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 9 AS a, 'x' AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot rename column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 10 AS a, 1 AS b2; -- error
+SELECT * FROM mvtest_replace;
+
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 11 AS a, 1 AS b, 'y' COLLATE "C" AS c;
+SELECT * FROM mvtest_replace;
+
+-- cannot change column collation
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 12 AS a, 1 AS b, 'x' COLLATE "POSIX" AS c; -- error
+SELECT * FROM mvtest_replace;
+
+-- cannot drop column
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 13 AS a, 1 AS b; -- error
+SELECT * FROM mvtest_replace;
+
+-- must target a matview
+CREATE VIEW mvtest_not_mv AS
+  SELECT 1 AS a;
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_not_mv AS
+  SELECT 1 AS a; -- error
+DROP VIEW mvtest_not_mv;
+
+-- cannot use OR REPLACE with IF NOT EXISTS
+CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
+  SELECT 1 AS a;
+
+DROP MATERIALIZED VIEW mvtest_replace;
-- 
2.50.1

From 21beeed4c89aa6e77e2e81de87f57cc33feaa7ef Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Tue, 5 Aug 2025 00:05:43 +0200
Subject: [PATCH v7 2/3] Handle default tablespace in AlterTableInternal

Move handling of default tablespace for CREATE OR REPLACE MATERIALIZED
VIEW from create_ctas_internal to ATPrepSetTableSpace.  It feels cleaner
that way in my opinion by not having to resolve the tablespace name just
to pass it to AlterTableInternal.  The default table space is passed as
empty string to AlterTableInternal.
---
 src/backend/commands/createas.c  | 21 ++-------------------
 src/backend/commands/tablecmds.c | 14 ++++++++++++--
 2 files changed, 14 insertions(+), 21 deletions(-)

diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 1620273f965..30ca0a21903 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -24,7 +24,6 @@
  */
 #include "postgres.h"
 
-#include "miscadmin.h"
 #include "access/heapam.h"
 #include "access/reloptions.h"
 #include "access/tableam.h"
@@ -35,7 +34,6 @@
 #include "commands/matview.h"
 #include "commands/prepare.h"
 #include "commands/tablecmds.h"
-#include "commands/tablespace.h"
 #include "commands/view.h"
 #include "executor/execdesc.h"
 #include "executor/executor.h"
@@ -160,23 +158,8 @@ create_ctas_internal(List *attrList, IntoClause *into)
 		/* tablespace */
 		atcmd = makeNode(AlterTableCmd);
 		atcmd->subtype = AT_SetTableSpace;
-		if (into->tableSpaceName != NULL)
-			atcmd->name = into->tableSpaceName;
-		else
-		{
-			Oid spcid;
-
-			/*
-			 * Resolve the name of the default or database tablespace because
-			 * we need to specify the tablespace by name.
-			 *
-			 * TODO: Move that to ATPrepSetTableSpace? Must allow AlterTableCmd.name to be NULL then.
-			 */
-			spcid = GetDefaultTablespace(RELPERSISTENCE_PERMANENT, false);
-			if (!OidIsValid(spcid))
-				spcid = MyDatabaseTableSpace;
-			atcmd->name = get_tablespace_name(spcid);
-		}
+		/* use empty string to specify default tablespace */
+		atcmd->name = into->tableSpaceName ? into->tableSpaceName : "";
 		atcmds = lappend(atcmds, atcmd);
 
 		/* storage options */
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 44dcd2c5b0d..6ec0b87f841 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -16580,8 +16580,18 @@ ATPrepSetTableSpace(AlteredTableInfo *tab, Relation rel, const char *tablespacen
 {
 	Oid			tablespaceId;
 
-	/* Check that the tablespace exists */
-	tablespaceId = get_tablespace_oid(tablespacename, false);
+	if (tablespacename != NULL && tablespacename[0] == '\0')
+	{
+		/* Use default tablespace if name is empty string */
+		tablespaceId = GetDefaultTablespace(rel->rd_rel->relpersistence, rel->rd_rel->relispartition);
+		if (!OidIsValid(tablespaceId))
+			tablespaceId = MyDatabaseTableSpace;
+	}
+	else
+	{
+		/* Check that the tablespace exists */
+		tablespaceId = get_tablespace_oid(tablespacename, false);
+	}
 
 	/* Check permissions except when moving to database's default */
 	if (OidIsValid(tablespaceId) && tablespaceId != MyDatabaseTableSpace)
-- 
2.50.1

From 01e073f5f1af495ba0559c08ad5ae1902a3ea593 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
Date: Fri, 26 Jul 2024 23:33:15 +0200
Subject: [PATCH v7 3/3] Add WITH OLD DATA to CREATE OR REPLACE MATERIALIZED
 VIEW

This keeps the matview populated when replacing its definition.
---
 .../sgml/ref/create_materialized_view.sgml    | 15 ++++++++--
 src/backend/commands/createas.c               | 29 +++++++++++++------
 src/backend/parser/gram.y                     | 16 ++++++++++
 src/include/nodes/primnodes.h                 |  1 +
 src/test/regress/expected/matview.out         | 22 ++++++++++++++
 src/test/regress/sql/matview.sql              | 13 +++++++++
 6 files changed, 84 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/create_materialized_view.sgml b/doc/src/sgml/ref/create_materialized_view.sgml
index 5e03320eb73..5b82af2ac70 100644
--- a/doc/src/sgml/ref/create_materialized_view.sgml
+++ b/doc/src/sgml/ref/create_materialized_view.sgml
@@ -27,7 +27,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
     [ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
     [ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
     AS <replaceable>query</replaceable>
-    [ WITH [ NO ] DATA ]
+    [ WITH [ NO | OLD ] DATA ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -37,7 +37,8 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
   <para>
    <command>CREATE MATERIALIZED VIEW</command> defines a materialized view of
    a query.  The query is executed and used to populate the view at the time
-   the command is issued (unless <command>WITH NO DATA</command> is used) and may be
+   the command is issued (unless <command>WITH NO DATA</command> or
+   <command>WITH OLD DATA</command> is used) and may be
    refreshed later using <command>REFRESH MATERIALIZED VIEW</command>.
   </para>
 
@@ -162,7 +163,7 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
    </varlistentry>
 
    <varlistentry>
-    <term><literal>WITH [ NO ] DATA</literal></term>
+    <term><literal>WITH [ NO | OLD ] DATA</literal></term>
     <listitem>
      <para>
       This clause specifies whether or not the materialized view should be
@@ -170,6 +171,14 @@ CREATE [ OR REPLACE ] MATERIALIZED VIEW [ IF NOT EXISTS ] <replaceable>table_nam
       flagged as unscannable and cannot be queried until <command>REFRESH
       MATERIALIZED VIEW</command> is used.
      </para>
+
+     <para>
+      The form <command>WITH OLD DATA</command> keeps the already stored data
+      when replacing an existing materialized view to keep it populated.  Use
+      this form if you want to use <command>REFRESH MATERIALIZED VIEW CONCURRENTLY</command>
+      as it requires a populated materialized view.  It is an error to use this
+      form when creating a new materialized view.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 30ca0a21903..ac2491fe01c 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -329,18 +329,26 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* An existing materialized view can be replaced. */
 		if (is_matview && into->replace)
 		{
-			RefreshMatViewStmt *refresh;
-
 			/* Change the relation to match the new query and other options. */
-			(void) create_ctas_nodata(query->targetList, into);
+			address = create_ctas_nodata(query->targetList, into);
+
+			/*
+			 * Refresh the materialized view with a fake statement unless we
+			 * must keep the old data.
+			 */
+			if (!into->keepData)
+			{
+				RefreshMatViewStmt *refresh;
+
+				refresh = makeNode(RefreshMatViewStmt);
+				refresh->relation = into->rel;
+				refresh->skipData = into->skipData;
+				refresh->concurrent = false;
 
-			/* Refresh the materialized view with a fake statement. */
-			refresh = makeNode(RefreshMatViewStmt);
-			refresh->relation = into->rel;
-			refresh->skipData = into->skipData;
-			refresh->concurrent = false;
+				address = ExecRefreshMatView(refresh, pstate->p_sourcetext, qc);
+			}
 
-			return ExecRefreshMatView(refresh, pstate->p_sourcetext, qc);
+			return address;
 		}
 
 		return InvalidObjectAddress;
@@ -383,6 +391,9 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 	 */
 	if (is_matview)
 	{
+		if (into->keepData)
+			elog(ERROR, "must not specify WITH OLD DATA when creating a new materialized view");
+
 		do_refresh = !into->skipData;
 		into->skipData = true;
 	}
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 7aaf0e37ad8..e51ce2701be 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -4944,6 +4944,22 @@ CreateMatViewStmt:
 					$7->replace = true;
 					$$ = (Node *) ctas;
 				}
+		| CREATE OR REPLACE OptNoLog MATERIALIZED VIEW create_mv_target AS SelectStmt WITH OLD DATA_P
+				{
+					CreateTableAsStmt *ctas = makeNode(CreateTableAsStmt);
+
+					ctas->query = $9;
+					ctas->into = $7;
+					ctas->objtype = OBJECT_MATVIEW;
+					ctas->is_select_into = false;
+					ctas->if_not_exists = false;
+					/* cram additional flags into the IntoClause */
+					$7->rel->relpersistence = $4;
+					$7->skipData = false;
+					$7->keepData = true;
+					$7->replace = true;
+					$$ = (Node *) ctas;
+				}
 		;
 
 create_mv_target:
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 3a0c3b06c81..e4c52ab05b4 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -169,6 +169,7 @@ typedef struct IntoClause
 	/* materialized view's SELECT query */
 	struct Query *viewQuery pg_node_attr(query_jumble_ignore);
 	bool		skipData;		/* true for WITH NO DATA */
+	bool		keepData;		/* true for WITH OLD DATA */
 	bool		replace;		/* replace existing matview? */
 } IntoClause;
 
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 56104b7ee8b..39b3a7c941c 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -731,6 +731,23 @@ SELECT * FROM mvtest_replace;
  3
 (1 row)
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 3
+(1 row)
+
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+ a 
+---
+ 5
+(1 row)
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -899,3 +916,8 @@ ERROR:  syntax error at or near "NOT"
 LINE 1: CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_rep...
                                                ^
 DROP MATERIALIZED VIEW mvtest_replace;
+-- Clause WITH OLD DATA is not allowed when creating a new matview.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA; -- error
+ERROR:  must not specify WITH OLD DATA when creating a new materialized view
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index fe0cb4d25bf..fb2e5f4b589 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -338,6 +338,14 @@ SELECT * FROM mvtest_replace; -- error: not populated
 REFRESH MATERIALIZED VIEW mvtest_replace;
 SELECT * FROM mvtest_replace;
 
+-- replace query but keep old data
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 5 AS a
+  WITH OLD DATA;
+SELECT * FROM mvtest_replace;
+REFRESH MATERIALIZED VIEW mvtest_replace;
+SELECT * FROM mvtest_replace;
+
 -- add column
 CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
   SELECT 4 AS a, 1 b;
@@ -431,3 +439,8 @@ CREATE OR REPLACE MATERIALIZED VIEW IF NOT EXISTS mvtest_replace AS
   SELECT 1 AS a;
 
 DROP MATERIALIZED VIEW mvtest_replace;
+
+-- Clause WITH OLD DATA is not allowed when creating a new matview.
+CREATE OR REPLACE MATERIALIZED VIEW mvtest_replace AS
+  SELECT 17 AS a
+  WITH OLD DATA; -- error
-- 
2.50.1