[patch] ALTER COLUMN SET EXPRESSION [GENERATED|STORED]

From 2ab10d94ca9bbc388bb39b1f77d6ed4ec4f6b237 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Wed, 12 Nov 2025 15:41:59 +0800
Subject: [PATCH v2 1/1] ALTER COLUMN SET EXPRESSION [GENERATED|STORED]

example explanation:
ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3);
nohting changed, work as is.

ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;
column b attgenerated will set to ATTRIBUTE_GENERATED_STORED,
column b is stored generated column now, table rewrite will happen.

ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
column b attgenerated will set to ATTRIBUTE_GENERATED_VIRTUAL,
column b is virtual generated column now,
table rewrite will not happen.

context: https://git.postgresql.org/cgit/postgresql.git/commit/?id=83ea6c54025bea67bcd4949a6d58d3fc11c3e21b
discussion: https://postgr.es/m/CACJufxGXLU400QBBgdoboaza0xK58rQqsCAPrxbAMUmo0f8xCQ@mail.gmail.com
---
 doc/src/sgml/ref/alter_table.sgml             |  21 ++-
 src/backend/access/heap/heapam_handler.c      |  12 ++
 src/backend/commands/tablecmds.c              | 141 +++++++++++++++++-
 src/backend/parser/gram.y                     |  28 ++++
 src/include/nodes/parsenodes.h                |   8 +
 .../test_ddl_deparse/expected/alter_table.out |   9 ++
 .../test_ddl_deparse/sql/alter_table.sql      |   3 +
 .../test_ddl_deparse/test_ddl_deparse.c       |  15 +-
 src/test/regress/expected/fast_default.out    |  12 ++
 .../regress/expected/generated_stored.out     | 138 +++++++++++++++++
 .../regress/expected/generated_virtual.out    | 123 +++++++++++++++
 src/test/regress/expected/publication.out     |   3 +
 src/test/regress/sql/fast_default.sql         |  10 ++
 src/test/regress/sql/generated_stored.sql     |  62 ++++++++
 src/test/regress/sql/generated_virtual.sql    |  41 +++++
 src/test/regress/sql/publication.sql          |   2 +
 src/tools/pgindent/typedefs.list              |   1 +
 17 files changed, 618 insertions(+), 11 deletions(-)

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 9d23ad5a0fb..910466430ee 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -46,7 +46,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET DEFAULT <replaceable class="parameter">expression</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP DEFAULT
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET | DROP } NOT NULL
-    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> )
+    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> ) [STORED | VIRTUAL]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP EXPRESSION [ IF EXISTS ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET GENERATED { ALWAYS | BY DEFAULT } | SET <replaceable>sequence_option</replaceable> | RESTART [ [ WITH ] <replaceable class="parameter">restart</replaceable> ] } [...]
@@ -266,16 +266,25 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry id="sql-altertable-desc-set-expression">
-    <term><literal>SET EXPRESSION AS</literal></term>
+    <term><literal>SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> ) <optional>STORED | VIRTUAL </optional> </literal></term>
     <listitem>
      <para>
-      This form replaces the expression of a generated column.  Existing data
-      in a stored generated column is rewritten and all the future changes
-      will apply the new generation expression.
+      This form replaces the expression of a generated column and optionally modify its storage persistence type.
+      If <literal>STORED</literal> is specified or the column is stored generated column,
+      existing data is rewritten and all the future changes will apply the new generation expression.
      </para>
 
      <para>
-      When this form is used on a stored generated column, its statistics
+      If <literal>VIRTUAL</literal> is specified, existing data won’t be rewritten,
+      and <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attgenerated</structfield>
+      is set to <literal>v</literal>.
+      If <literal>STORED</literal> is specified,
+      <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attgenerated</structfield>
+      set to <literal>s</literal>.
+     </para>
+
+     <para>
+      When this form is used on a stored generated column or <literal>STORED</literal> is specified, its statistics
       are removed, so running
       <link linkend="sql-analyze"><command>ANALYZE</command></link>
       on the table afterwards is recommended.
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index bcbac844bb6..3f704ef284e 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -2375,6 +2375,10 @@ heapam_scan_sample_next_tuple(TableScanDesc scan, SampleScanState *scanstate,
  * currently only known to happen as an after-effect of ALTER TABLE
  * SET WITHOUT OIDS.
  *
+ * 3. ALTER TABLE SET EXPRESSION VIRTUAL may make a stored generated column to a
+ *    virtual one; in that case, the corresponding tuple value needs to be set
+ *    to NULL.
+ *
  * So, we must reconstruct the tuple from component Datums.
  */
 static void
@@ -2394,6 +2398,14 @@ reform_and_rewrite_tuple(HeapTuple tuple,
 	{
 		if (TupleDescCompactAttr(newTupDesc, i)->attisdropped)
 			isnull[i] = true;
+		if (TupleDescCompactAttr(newTupDesc, i)->attgenerated)
+		{
+			if (TupleDescAttr(newTupDesc, i)->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL)
+			{
+				values[i] = (Datum) 0;
+				isnull[i] = true;
+			}
+		}
 	}
 
 	copiedTuple = heap_form_tuple(newTupDesc, values, isnull);
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 23ebaa3f230..bbd6cb15fd2 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -523,6 +523,7 @@ static ObjectAddress ATExecDropIdentity(Relation rel, const char *colName, bool
 static ObjectAddress ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 										 Node *newExpr, LOCKMODE lockmode);
 static void ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode);
+static void ATPrepSetExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode);
 static ObjectAddress ATExecDropExpression(Relation rel, const char *colName, bool missing_ok, LOCKMODE lockmode);
 static ObjectAddress ATExecSetStatistics(Relation rel, const char *colName, int16 colNum,
 										 Node *newValue, LOCKMODE lockmode);
@@ -5021,6 +5022,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			ATSimplePermissions(cmd->subtype, rel,
 								ATT_TABLE | ATT_PARTITIONED_TABLE | ATT_FOREIGN_TABLE);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode, context);
+			ATPrepSetExpression(rel, cmd, recurse, recursing, lockmode);
 			pass = AT_PASS_SET_EXPRESSION;
 			break;
 		case AT_DropExpression: /* ALTER COLUMN DROP EXPRESSION */
@@ -8604,8 +8606,9 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	Expr	   *defval;
 	NewColumnValue *newval;
 	RawColumnDefault *rawEnt;
+	Node	   *raw_default;
 
-	tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
+	tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);
 	if (!HeapTupleIsValid(tuple))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_COLUMN),
@@ -8632,7 +8635,7 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	 * TODO: This could be done, just need to recheck any constraints
 	 * afterwards.
 	 */
-	if (attgenerated == ATTRIBUTE_GENERATED_VIRTUAL &&
+	if (!IsA(newExpr, GenerationExpr) && attgenerated == ATTRIBUTE_GENERATED_VIRTUAL &&
 		rel->rd_att->constr && rel->rd_att->constr->num_check > 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -8660,7 +8663,75 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 
 	rewrite = (attgenerated == ATTRIBUTE_GENERATED_STORED);
 
-	ReleaseSysCache(tuple);
+	/*
+	 * ALTER TABLE ALTER COLUMN SET EXPRESSION STORED/VIRTUAL
+	 * Change the generation expression, may also change the attgenerated.
+	 */
+	if (IsA(newExpr, GenerationExpr))
+	{
+		GenerationExpr   *g = (GenerationExpr *) newExpr;
+
+		raw_default = g->raw_expr;
+
+		if (attgenerated != g->generated_kind)
+		{
+			Relation	pg_attribute;
+
+			attgenerated = g->generated_kind;
+			attTup->attgenerated = g->generated_kind;
+			if (g->generated_kind == ATTRIBUTE_GENERATED_VIRTUAL)
+			{
+				RememberAllDependentForRebuilding(tab, AT_SetExpression, rel, attnum, colName);
+
+				/*
+				 * Virtual generated columns currently do not support indexes,
+				 * statistics, user-defined types, or publications.
+				 */
+				if (tab->changedIndexOids != NIL)
+					ereport(ERROR,
+							errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("cannot changed generated column (%s) from STORED to VIRTUAL", colName),
+							errdetail("indexes on virtual generated columns are not supported."));
+
+				if (tab->changedStatisticsOids != NIL)
+					ereport(ERROR,
+							errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("cannot changed generated column (%s) from STORED to VIRTUAL", colName),
+							errdetail("statistics creation on virtual generated columns is not supported."));
+
+				if (attTup->atttypid >= FirstUnpinnedObjectId)
+					ereport(ERROR,
+							errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("cannot changed generated column (%s) from STORED to VIRTUAL", colName),
+							errdetail("Virtual generated columns that make use of user-defined types are not yet supported."));
+
+				if (GetRelationPublications(RelationGetRelid(rel)) != NIL)
+					ereport(ERROR,
+							errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("cannot changed generated column (%s) from STORED to VIRTUAL", colName),
+							errmsg("ALTER TABLE / SET EXPRESSION is not supported for virtual generated columns in tables that are part of a publication"));
+				/*
+				 * change a stored generated column to virtual no need table
+				 * rewrite
+				 */
+				rewrite = false;
+			}
+			else
+				rewrite = true;
+
+			pg_attribute = table_open(AttributeRelationId, RowExclusiveLock);
+			CatalogTupleUpdate(pg_attribute, &tuple->t_self, tuple);
+
+			InvokeObjectPostAlterHook(RelationRelationId,
+									  RelationGetRelid(rel),
+									  attnum);
+			table_close(pg_attribute, RowExclusiveLock);
+		}
+	}
+	else
+		raw_default = newExpr;
+
+	heap_freetuple(tuple);
 
 	if (rewrite)
 	{
@@ -8706,7 +8777,7 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	/* Prepare to store the new expression, in the catalogs */
 	rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
 	rawEnt->attnum = attnum;
-	rawEnt->raw_default = newExpr;
+	rawEnt->raw_default = raw_default;
 	rawEnt->generated = attgenerated;
 
 	/* Store the generated expression */
@@ -8787,6 +8858,68 @@ ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recurs
 	}
 }
 
+/*
+ * ALTER TABLE ALTER COLUMN SET EXPRESSION [STORED | VIRTUAL]
+ *
+ * This needs to recurse into all child tables; otherwise, the parent and child
+ * may end up with different storage types for the generated column.
+ */
+static void
+ ATPrepSetExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode)
+{
+	/*
+	 * Reject ONLY if there are child tables.
+	 */
+	if (!recurse && !recursing &&
+		IsA(cmd->def, GenerationExpr) &&
+		find_inheritance_children(RelationGetRelid(rel), lockmode))
+	{
+		GenerationExpr *genexpr = castNode(GenerationExpr, cmd->def);
+		if (genexpr->generated_kind == ATTRIBUTE_GENERATED_STORED)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("ALTER TABLE ... SET EXPRESSION STORED must be applied to child tables too"),
+					errhint("Do not specify the ONLY keyword."));
+		else
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("ALTER TABLE ... SET EXPRESSION VIRTUAL must be applied to child tables too"),
+					errhint("Do not specify the ONLY keyword."));
+	}
+
+	/*
+	 * Cannot change generation expression kind from inherited columns.
+	 */
+	if (!recursing && IsA(cmd->def, GenerationExpr))
+	{
+		HeapTuple	tuple;
+		Form_pg_attribute attTup;
+
+		tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), cmd->name);
+		if (!HeapTupleIsValid(tuple))
+			ereport(ERROR,
+					errcode(ERRCODE_UNDEFINED_COLUMN),
+					errmsg("column \"%s\" of relation \"%s\" does not exist",
+						   cmd->name, RelationGetRelationName(rel)));
+
+		attTup = (Form_pg_attribute) GETSTRUCT(tuple);
+
+		if (attTup->attinhcount > 0)
+		{
+			GenerationExpr *genexpr = castNode(GenerationExpr, cmd->def);
+
+			if (genexpr->generated_kind == ATTRIBUTE_GENERATED_STORED)
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column"));
+			else
+				ereport(ERROR,
+						errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+						errmsg("cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column"));
+		}
+	}
+}
+
 /*
  * Return the address of the affected column.
  */
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 57fe0186547..8a9a0b238ba 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -2524,6 +2524,34 @@ alter_table_cmd:
 					n->def = $8;
 					$$ = (Node *) n;
 				}
+			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET EXPRESSION AS <expr> VIRTUAL */
+			| ALTER opt_column ColId SET EXPRESSION AS '(' a_expr ')' VIRTUAL
+				{
+					AlterTableCmd *n = makeNode(AlterTableCmd);
+					GenerationExpr *g = makeNode(GenerationExpr);
+
+					g->raw_expr = $8;
+					g->generated_kind = ATTRIBUTE_GENERATED_VIRTUAL;
+
+					n->subtype = AT_SetExpression;
+					n->name = $3;
+					n->def = (Node *) g;
+					$$ = (Node *) n;
+				}
+			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET EXPRESSION AS <expr> STORED */
+			| ALTER opt_column ColId SET EXPRESSION AS '(' a_expr ')' STORED
+				{
+					AlterTableCmd *n = makeNode(AlterTableCmd);
+					GenerationExpr *g = makeNode(GenerationExpr);
+
+					g->raw_expr = $8;
+					g->generated_kind = ATTRIBUTE_GENERATED_STORED;
+
+					n->subtype = AT_SetExpression;
+					n->name = $3;
+					n->def = (Node *) g;
+					$$ = (Node *) n;
+				}
 			/* ALTER TABLE <name> ALTER [COLUMN] <colname> DROP EXPRESSION */
 			| ALTER opt_column ColId DROP EXPRESSION
 				{
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index d14294a4ece..4f8a1520394 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2877,6 +2877,14 @@ typedef struct Constraint
 	ParseLoc	location;		/* token location, or -1 if unknown */
 } Constraint;
 
+typedef struct GenerationExpr
+{
+	NodeTag		type;
+	Node	   *raw_expr; 		/* generation expression as a
+								 * untransformed a_expr node */
+	char		generated_kind; /* STORED or VIRTUAL */
+} GenerationExpr;
+
 /* ----------------------
  *		Create/Drop Table Space Statements
  * ----------------------
diff --git a/src/test/modules/test_ddl_deparse/expected/alter_table.out b/src/test/modules/test_ddl_deparse/expected/alter_table.out
index 50d0354a341..a5fb293f357 100644
--- a/src/test/modules/test_ddl_deparse/expected/alter_table.out
+++ b/src/test/modules/test_ddl_deparse/expected/alter_table.out
@@ -122,6 +122,15 @@ CREATE TABLE tbl (
 	b text
 );
 NOTICE:  DDL test: type simple, tag CREATE TABLE
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2);
+NOTICE:  DDL test: type alter table, tag ALTER TABLE
+NOTICE:    subcommand: type SET EXPRESSION desc column a of table tbl
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) VIRTUAL;
+NOTICE:  DDL test: type alter table, tag ALTER TABLE
+NOTICE:    subcommand: type SET EXPRESSION VIRTUAL desc column a of table tbl
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) STORED;
+NOTICE:  DDL test: type alter table, tag ALTER TABLE
+NOTICE:    subcommand: type SET EXPRESSION STORED desc column a of table tbl
 ALTER TABLE tbl ALTER COLUMN a DROP EXPRESSION;
 NOTICE:  DDL test: type alter table, tag ALTER TABLE
 NOTICE:    subcommand: type DROP EXPRESSION desc column a of table tbl
diff --git a/src/test/modules/test_ddl_deparse/sql/alter_table.sql b/src/test/modules/test_ddl_deparse/sql/alter_table.sql
index 9ad1cf908d4..e29d108a8f7 100644
--- a/src/test/modules/test_ddl_deparse/sql/alter_table.sql
+++ b/src/test/modules/test_ddl_deparse/sql/alter_table.sql
@@ -67,6 +67,9 @@ CREATE TABLE tbl (
 	b text
 );
 
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2);
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) VIRTUAL;
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) STORED;
 ALTER TABLE tbl ALTER COLUMN a DROP EXPRESSION;
 
 ALTER TABLE tbl ALTER COLUMN b SET COMPRESSION pglz;
diff --git a/src/test/modules/test_ddl_deparse/test_ddl_deparse.c b/src/test/modules/test_ddl_deparse/test_ddl_deparse.c
index 193669f2bc1..d9dc87136e9 100644
--- a/src/test/modules/test_ddl_deparse/test_ddl_deparse.c
+++ b/src/test/modules/test_ddl_deparse/test_ddl_deparse.c
@@ -129,8 +129,21 @@ get_altertable_subcmdinfo(PG_FUNCTION_ARGS)
 				strtype = "SET NOT NULL";
 				break;
 			case AT_SetExpression:
-				strtype = "SET EXPRESSION";
+			{
+				if (IsA(subcmd->def, GenerationExpr))
+				{
+					GenerationExpr *genexpr = castNode(GenerationExpr, subcmd->def);
+
+					if (genexpr->generated_kind == ATTRIBUTE_GENERATED_STORED)
+						strtype = "SET EXPRESSION STORED";
+					else
+						strtype = "SET EXPRESSION VIRTUAL";
+				}
+				else
+					strtype = "SET EXPRESSION";
+
 				break;
+			}
 			case AT_DropExpression:
 				strtype = "DROP EXPRESSION";
 				break;
diff --git a/src/test/regress/expected/fast_default.out b/src/test/regress/expected/fast_default.out
index ccbcdf8403f..4d566550405 100644
--- a/src/test/regress/expected/fast_default.out
+++ b/src/test/regress/expected/fast_default.out
@@ -70,6 +70,18 @@ NOTICE:  rewriting table has_volatile for reason 4
 -- stored generated columns need a rewrite
 ALTER TABLE has_volatile ADD col7 int GENERATED ALWAYS AS (55) stored;
 NOTICE:  rewriting table has_volatile for reason 2
+-- change generated columns from virtual to stored need a rewrite
+ALTER TABLE has_volatile ADD col8 int GENERATED ALWAYS AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+NOTICE:  rewriting table has_volatile for reason 2
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+NOTICE:  rewriting table has_volatile for reason 2
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
+NOTICE:  rewriting table has_volatile for reason 2
+-- change generated columns from stored to virtual no need a rewrite
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
 -- Test a large sample of different datatypes
 CREATE TABLE T(pk INT NOT NULL PRIMARY KEY, c_int INT DEFAULT 1);
 SELECT set('t');
diff --git a/src/test/regress/expected/generated_stored.out b/src/test/regress/expected/generated_stored.out
index 8b7a71d8f0c..ea90d20ab1d 100644
--- a/src/test/regress/expected/generated_stored.out
+++ b/src/test/regress/expected/generated_stored.out
@@ -2,6 +2,12 @@
 CREATE SCHEMA generated_stored_tests;
 GRANT USAGE ON SCHEMA generated_stored_tests TO PUBLIC;
 SET search_path = generated_stored_tests;
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, atthasdef, pg_get_expr(pd.adbin, pa.attrelid)
+FROM    pg_attribute pa JOIN pg_attrdef pd
+ON      pd.adrelid = pa.attrelid
+WHERE   pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) STORED);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 SELECT table_name, column_name, column_default, is_nullable, is_generated, generation_expression FROM information_schema.columns WHERE table_schema = 'generated_stored_tests' ORDER BY 1, 2;
@@ -559,6 +565,11 @@ SELECT * FROM gtest_varlena ORDER BY a;
 (2 rows)
 
 DROP TABLE gtest_varlena;
+-- varlena types change from stored to virtual
+CREATE TABLE gtest_varlena (a int, b text STORAGE EXTERNAL GENERATED ALWAYS AS (repeat('g', a)) STORED);
+INSERT INTO  gtest_varlena VALUES(2001), (1);
+ALTER TABLE gtest_varlena ALTER COLUMN b SET EXPRESSION AS (repeat('g', a)) VIRTUAL;
+VACUUM(FULL) gtest_varlena; --should ok
 -- composite types
 CREATE TYPE double_int as (a int, b int);
 CREATE TABLE gtest4 (
@@ -573,6 +584,9 @@ SELECT * FROM gtest4;
  6 | (12,18)
 (2 rows)
 
+ALTER TABLE gtest4 ALTER COLUMN b SET EXPRESSION AS ((a * 2, a * 3)) VIRTUAL; --error
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  Virtual generated columns that make use of user-defined types are not yet supported.
 DROP TABLE gtest4;
 DROP TYPE double_int;
 -- using tableoid is allowed
@@ -666,6 +680,8 @@ ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated b
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 50); -- fails on existing row
 ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated by some row
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 61); -- ok
+ALTER TABLE gtest20a ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL; -- violates constraint
+ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated by some row
 CREATE TABLE gtest20b (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 INSERT INTO gtest20b (a) VALUES (10);
 INSERT INTO gtest20b (a) VALUES (30);
@@ -833,6 +849,9 @@ ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 5); -- error
 ERROR:  insert or update on table "gtest23b" violates foreign key constraint "gtest23b_b_fkey"
 DETAIL:  Key (b)=(5) is not present in table "gtest23a".
 ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 1); -- ok
+--error, virutal generated column does not support foreign key
+ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 11) VIRTUAL;
+ERROR:  foreign key constraints on virtual generated columns are not supported
 DROP TABLE gtest23b;
 DROP TABLE gtest23a;
 CREATE TABLE gtest23p (x int, y int GENERATED ALWAYS AS (x * 2) STORED, PRIMARY KEY (y));
@@ -858,6 +877,10 @@ CREATE TABLE gtest24nn (a int, b gtestdomainnn GENERATED ALWAYS AS (a * 2) STORE
 INSERT INTO gtest24nn (a) VALUES (4);  -- ok
 INSERT INTO gtest24nn (a) VALUES (NULL);  -- error
 ERROR:  value for domain gtestdomainnn violates check constraint "gtestdomainnn_check"
+--error, virutal generated column does not support domains
+ALTER TABLE gtest24nn ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  Virtual generated columns that make use of user-defined types are not yet supported.
 -- typed tables (currently not supported)
 CREATE TYPE gtest_type AS (f1 integer, f2 text, f3 bigint);
 CREATE TABLE gtest28 OF gtest_type (f1 WITH OPTIONS GENERATED ALWAYS AS (f2 *2) STORED);
@@ -980,7 +1003,17 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION STORED must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION VIRTUAL must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
 \d gtest_parent
            Partitioned table "generated_stored_tests.gtest_parent"
  Column |  Type  | Collation | Nullable |               Default               
@@ -1065,6 +1098,34 @@ Partition of: gtest_parent FOR VALUES FROM ('08-01-2016') TO ('09-01-2016')
  f3     | bigint |           |          | generated always as (f2 * 2) stored
 Partition of: gtest_parent FOR VALUES FROM ('09-01-2016') TO ('10-01-2016')
 
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+--------------+---------+--------+--------------+-----------+-------------
+ gtest_child  | f3      |      3 | v            | t         | (f2 * 11)
+ gtest_child2 | f3      |      3 | v            | t         | (f2 * 11)
+ gtest_child3 | f3      |      3 | v            | t         | (f2 * 11)
+ gtest_parent | f3      |      3 | v            | t         | (f2 * 11)
+(4 rows)
+
+SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
+   tableoid   |     f1     | f2 | f3 
+--------------+------------+----+----
+ gtest_child  | 07-15-2016 |  2 | 22
+ gtest_child2 | 08-15-2016 |  3 | 33
+ gtest_child3 | 09-13-2016 |  1 | 11
+(3 rows)
+
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+--------------+---------+--------+--------------+-----------+-------------
+ gtest_child  | f3      |      3 | s            | t         | (f2 * 2)
+ gtest_child2 | f3      |      3 | s            | t         | (f2 * 2)
+ gtest_child3 | f3      |      3 | s            | t         | (f2 * 2)
+ gtest_parent | f3      |      3 | s            | t         | (f2 * 2)
+(4 rows)
+
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
    tableoid   |     f1     | f2 | f3 
 --------------+------------+----+----
@@ -1141,6 +1202,10 @@ SELECT * FROM gtest25 ORDER BY a;
 Indexes:
     "gtest25_pkey" PRIMARY KEY, btree (a)
 
+--erorr, can not add and set generation expression in one statement
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
+ERROR:  column "d1" of relation "gtest25" does not exist
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
     a int,
@@ -1279,6 +1344,46 @@ ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 --------+---------+-----------+----------+---------
  b      | integer |           |          | 
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+DROP TABLE gtest29;
+CREATE TABLE gtest29 (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
+INSERT INTO gtest29 (a) VALUES (3), (4);
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+---------+---------+--------+--------------+-----------+-------------
+ gtest29 | b       |      2 | v            | t         | (a * 3)
+(1 row)
+
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  9
+ 4 | 12
+(2 rows)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+---------+---------+--------+--------------+-----------+-------------
+ gtest29 | b       |      2 | v            | t         | (a * 3)
+(1 row)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  9
+ 4 | 12
+(2 rows)
+
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+---------+---------+--------+--------------+-----------+-------------
+ gtest29 | b       |      2 | s            | t         | (a * 3)
+(1 row)
+
 -- with inheritance
 CREATE TABLE gtest30 (
     a int,
@@ -1329,6 +1434,27 @@ Inherits: gtest30
 
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
 ERROR:  cannot drop generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+-----------+---------+--------+--------------+-----------+-------------
+ gtest30   | b       |      2 | s            | t         | (a * 2)
+ gtest30_1 | b       |      2 | s            | t         | (a * 2)
+(2 rows)
+
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+-----------+---------+--------+--------------+-----------+-------------
+ gtest30   | b       |      2 | v            | t         | (a * 2)
+ gtest30_1 | b       |      2 | v            | t         | (a * 2)
+(2 rows)
+
+DEALLOCATE get_generated_info;
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
@@ -1347,6 +1473,18 @@ CREATE INDEX gtest31_2_y_idx ON gtest31_2(((y).b));
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello3');
 ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row type
 DROP TABLE gtest31_1, gtest31_2;
+CREATE TABLE gtest31_1 (a int, b int GENERATED ALWAYS AS (a) STORED);
+CREATE STATISTICS gtest31_2_stat ON (b IS NOT NULL) FROM gtest31_1;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) STORED; --ok
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  statistics creation on virtual generated columns is not supported.
+DROP STATISTICS gtest31_2_stat;
+CREATE INDEX ON gtest31_1(b);
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  indexes on virtual generated columns are not supported.
+DROP TABLE gtest31_1;
 -- Check it for a partitioned table, too
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text) PARTITION BY LIST (a);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
diff --git a/src/test/regress/expected/generated_virtual.out b/src/test/regress/expected/generated_virtual.out
index dde325e46c6..f1960b18a96 100644
--- a/src/test/regress/expected/generated_virtual.out
+++ b/src/test/regress/expected/generated_virtual.out
@@ -2,6 +2,12 @@
 CREATE SCHEMA generated_virtual_tests;
 GRANT USAGE ON SCHEMA generated_virtual_tests TO PUBLIC;
 SET search_path = generated_virtual_tests;
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, atthasdef,  pg_get_expr(pd.adbin, pa.attrelid)
+FROM  pg_attribute pa JOIN pg_attrdef pd
+ON pd.adrelid = pa.attrelid
+WHERE pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) VIRTUAL);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 SELECT table_name, column_name, column_default, is_nullable, is_generated, generation_expression FROM information_schema.columns WHERE table_schema = 'generated_virtual_tests' ORDER BY 1, 2;
@@ -645,6 +651,20 @@ DETAIL:  Column "b" of relation "gtest20" is a virtual generated column.
 ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3);  -- ok (currently not supported)
 ERROR:  ALTER TABLE / SET EXPRESSION is not supported for virtual generated columns in tables with check constraints
 DETAIL:  Column "b" of relation "gtest20" is a virtual generated column.
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 5) STORED;  --error, violates constraint
+ERROR:  check constraint "gtest20_b_check" of relation "gtest20" is violated by some row
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;  --ok
+\d gtest20
+                   Table "generated_virtual_tests.gtest20"
+ Column |  Type   | Collation | Nullable |              Default               
+--------+---------+-----------+----------+------------------------------------
+ a      | integer |           | not null | 
+ b      | integer |           |          | generated always as (a * 3) stored
+Indexes:
+    "gtest20_pkey" PRIMARY KEY, btree (a)
+Check constraints:
+    "gtest20_b_check" CHECK (b < 50)
+
 CREATE TABLE gtest20a (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 INSERT INTO gtest20a (a) VALUES (10);
 INSERT INTO gtest20a (a) VALUES (30);
@@ -943,6 +963,17 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+-- SET EXPRESSION VIRTUAL | STORED need apply to all inherited tables
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION STORED must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION VIRTUAL must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
 \d gtest_parent
        Partitioned table "generated_virtual_tests.gtest_parent"
  Column |  Type  | Collation | Nullable |           Default            
@@ -1027,6 +1058,34 @@ Partition of: gtest_parent FOR VALUES FROM ('08-01-2016') TO ('09-01-2016')
  f3     | bigint |           |          | generated always as (f2 * 2)
 Partition of: gtest_parent FOR VALUES FROM ('09-01-2016') TO ('10-01-2016')
 
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+--------------+---------+--------+--------------+-----------+-------------
+ gtest_child  | f3      |      3 | s            | t         | (f2 * 11)
+ gtest_child2 | f3      |      3 | s            | t         | (f2 * 11)
+ gtest_child3 | f3      |      3 | s            | t         | (f2 * 11)
+ gtest_parent | f3      |      3 | s            | t         | (f2 * 11)
+(4 rows)
+
+SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
+   tableoid   |     f1     | f2 | f3 
+--------------+------------+----+----
+ gtest_child  | 07-15-2016 |  2 | 22
+ gtest_child2 | 08-15-2016 |  3 | 33
+ gtest_child3 | 09-13-2016 |  1 | 11
+(3 rows)
+
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+--------------+---------+--------+--------------+-----------+-------------
+ gtest_child  | f3      |      3 | v            | t         | (f2 * 2)
+ gtest_child2 | f3      |      3 | v            | t         | (f2 * 2)
+ gtest_child3 | f3      |      3 | v            | t         | (f2 * 2)
+ gtest_parent | f3      |      3 | v            | t         | (f2 * 2)
+(4 rows)
+
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
    tableoid   |     f1     | f2 | f3 
 --------------+------------+----+----
@@ -1103,6 +1162,10 @@ SELECT * FROM gtest25 ORDER BY a;
 Indexes:
     "gtest25_pkey" PRIMARY KEY, btree (a)
 
+--erorr, can not add and set generation expression in one statement
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
+ERROR:  column "d1" of relation "gtest25" does not exist
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
     a int,
@@ -1244,6 +1307,45 @@ SELECT * FROM gtest29;
  a      | integer |           |          | 
  b      | integer |           |          | generated always as (a * 3)
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+---------+---------+--------+--------------+-----------+-------------
+ gtest29 | b       |      2 | s            | t         | (a * 3)
+(1 row)
+
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  9
+ 4 | 12
+ 5 | 15
+(3 rows)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+---------+---------+--------+--------------+-----------+-------------
+ gtest29 | b       |      2 | s            | t         | (a * 3)
+(1 row)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+---------+---------+--------+--------------+-----------+-------------
+ gtest29 | b       |      2 | v            | t         | (a * 3)
+(1 row)
+
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  9
+ 4 | 12
+ 5 | 15
+(3 rows)
+
 -- check that dependencies between columns have also been removed
 --ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 --\d gtest29
@@ -1299,6 +1401,27 @@ Inherits: gtest30
 
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
 ERROR:  cannot drop generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+-----------+---------+--------+--------------+-----------+-------------
+ gtest30   | b       |      2 | s            | t         | (a * 2)
+ gtest30_1 | b       |      2 | s            | t         | (a * 2)
+(2 rows)
+
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | atthasdef | pg_get_expr 
+-----------+---------+--------+--------------+-----------+-------------
+ gtest30   | b       |      2 | v            | t         | (a * 2)
+ gtest30_1 | b       |      2 | v            | t         | (a * 2)
+(2 rows)
+
+DEALLOCATE get_generated_info;
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') VIRTUAL, c text);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
diff --git a/src/test/regress/expected/publication.out b/src/test/regress/expected/publication.out
index e72d1308967..22161160427 100644
--- a/src/test/regress/expected/publication.out
+++ b/src/test/regress/expected/publication.out
@@ -882,6 +882,9 @@ DETAIL:  Column list used by the publication does not cover the replica identity
 ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 -- ok: stored generated column "d" can be in the list too
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, d);
+--error
+ALTER TABLE testpub_tbl5 ALTER COLUMN d SET EXPRESSION AS (a + length(b)) VIRTUAL;
+ERROR:  ALTER TABLE / SET EXPRESSION is not supported for virtual generated columns in tables that are part of a publication
 ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 -- error: virtual generated column "e" can't be in list
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, e);
diff --git a/src/test/regress/sql/fast_default.sql b/src/test/regress/sql/fast_default.sql
index 068dd0bc8aa..2a8ae18d2b8 100644
--- a/src/test/regress/sql/fast_default.sql
+++ b/src/test/regress/sql/fast_default.sql
@@ -77,6 +77,16 @@ ALTER TABLE has_volatile ALTER COLUMN col1 SET DATA TYPE float8,
 -- stored generated columns need a rewrite
 ALTER TABLE has_volatile ADD col7 int GENERATED ALWAYS AS (55) stored;
 
+-- change generated columns from virtual to stored need a rewrite
+ALTER TABLE has_volatile ADD col8 int GENERATED ALWAYS AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
+
+-- change generated columns from stored to virtual no need a rewrite
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
 
 
 -- Test a large sample of different datatypes
diff --git a/src/test/regress/sql/generated_stored.sql b/src/test/regress/sql/generated_stored.sql
index 2001a47bcc6..960e91b8b66 100644
--- a/src/test/regress/sql/generated_stored.sql
+++ b/src/test/regress/sql/generated_stored.sql
@@ -5,6 +5,13 @@ CREATE SCHEMA generated_stored_tests;
 GRANT USAGE ON SCHEMA generated_stored_tests TO PUBLIC;
 SET search_path = generated_stored_tests;
 
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, atthasdef, pg_get_expr(pd.adbin, pa.attrelid)
+FROM    pg_attribute pa JOIN pg_attrdef pd
+ON      pd.adrelid = pa.attrelid
+WHERE   pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
+
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) STORED);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 
@@ -251,6 +258,12 @@ INSERT INTO gtest_varlena (a) VALUES(NULL);
 SELECT * FROM gtest_varlena ORDER BY a;
 DROP TABLE gtest_varlena;
 
+-- varlena types change from stored to virtual
+CREATE TABLE gtest_varlena (a int, b text STORAGE EXTERNAL GENERATED ALWAYS AS (repeat('g', a)) STORED);
+INSERT INTO  gtest_varlena VALUES(2001), (1);
+ALTER TABLE gtest_varlena ALTER COLUMN b SET EXPRESSION AS (repeat('g', a)) VIRTUAL;
+VACUUM(FULL) gtest_varlena; --should ok
+
 -- composite types
 CREATE TYPE double_int as (a int, b int);
 CREATE TABLE gtest4 (
@@ -260,6 +273,7 @@ CREATE TABLE gtest4 (
 INSERT INTO gtest4 VALUES (1), (6);
 SELECT * FROM gtest4;
 
+ALTER TABLE gtest4 ALTER COLUMN b SET EXPRESSION AS ((a * 2, a * 3)) VIRTUAL; --error
 DROP TABLE gtest4;
 DROP TYPE double_int;
 
@@ -326,6 +340,7 @@ ALTER TABLE gtest20a ADD CHECK (b < 50);  -- fails on existing row
 -- table rewrite cases
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 50); -- fails on existing row
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 61); -- ok
+ALTER TABLE gtest20a ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL; -- violates constraint
 
 CREATE TABLE gtest20b (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 INSERT INTO gtest20b (a) VALUES (10);
@@ -403,6 +418,8 @@ INSERT INTO gtest23b VALUES (5);  -- error
 ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 5); -- error
 ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 1); -- ok
 
+--error, virutal generated column does not support foreign key
+ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 11) VIRTUAL;
 DROP TABLE gtest23b;
 DROP TABLE gtest23a;
 
@@ -428,6 +445,9 @@ CREATE TABLE gtest24nn (a int, b gtestdomainnn GENERATED ALWAYS AS (a * 2) STORE
 INSERT INTO gtest24nn (a) VALUES (4);  -- ok
 INSERT INTO gtest24nn (a) VALUES (NULL);  -- error
 
+--error, virutal generated column does not support domains
+ALTER TABLE gtest24nn ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+
 -- typed tables (currently not supported)
 CREATE TYPE gtest_type AS (f1 integer, f2 text, f3 bigint);
 CREATE TABLE gtest28 OF gtest_type (f1 WITH OPTIONS GENERATED ALWAYS AS (f2 *2) STORED);
@@ -486,7 +506,11 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
 \d gtest_parent
 \d gtest_child
 \d gtest_child2
@@ -499,6 +523,11 @@ ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2);
 \d gtest_child
 \d gtest_child2
 \d gtest_child3
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- we leave these tables around for purposes of testing dump/reload/upgrade
 
@@ -523,6 +552,9 @@ ALTER TABLE gtest25 ALTER COLUMN d SET DATA TYPE float8,
   ADD COLUMN y float8 GENERATED ALWAYS AS (d * 4) STORED;
 SELECT * FROM gtest25 ORDER BY a;
 \d gtest25
+--erorr, can not add and set generation expression in one statement
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
 
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
@@ -578,6 +610,20 @@ SELECT * FROM gtest29;
 ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 \d gtest29
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+DROP TABLE gtest29;
+CREATE TABLE gtest29 (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
+INSERT INTO gtest29 (a) VALUES (3), (4);
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+SELECT * FROM gtest29;
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;
+SELECT * FROM gtest29;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+
 -- with inheritance
 CREATE TABLE gtest30 (
     a int,
@@ -597,6 +643,13 @@ ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION;  -- error
 \d gtest30
 \d gtest30_1
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+DEALLOCATE get_generated_info;
 
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text);
@@ -617,6 +670,15 @@ ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello3');
 
 DROP TABLE gtest31_1, gtest31_2;
 
+CREATE TABLE gtest31_1 (a int, b int GENERATED ALWAYS AS (a) STORED);
+CREATE STATISTICS gtest31_2_stat ON (b IS NOT NULL) FROM gtest31_1;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) STORED; --ok
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+DROP STATISTICS gtest31_2_stat;
+CREATE INDEX ON gtest31_1(b);
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+DROP TABLE gtest31_1;
+
 -- Check it for a partitioned table, too
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text) PARTITION BY LIST (a);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
diff --git a/src/test/regress/sql/generated_virtual.sql b/src/test/regress/sql/generated_virtual.sql
index 2911439776c..f25454821b8 100644
--- a/src/test/regress/sql/generated_virtual.sql
+++ b/src/test/regress/sql/generated_virtual.sql
@@ -5,6 +5,13 @@ CREATE SCHEMA generated_virtual_tests;
 GRANT USAGE ON SCHEMA generated_virtual_tests TO PUBLIC;
 SET search_path = generated_virtual_tests;
 
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, atthasdef,  pg_get_expr(pd.adbin, pa.attrelid)
+FROM  pg_attribute pa JOIN pg_attrdef pd
+ON pd.adrelid = pa.attrelid
+WHERE pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
+
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) VIRTUAL);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 
@@ -319,6 +326,9 @@ INSERT INTO gtest20 (a) VALUES (30);  -- violates constraint
 
 ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 100);  -- violates constraint (currently not supported)
 ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3);  -- ok (currently not supported)
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 5) STORED;  --error, violates constraint
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;  --ok
+\d gtest20
 
 CREATE TABLE gtest20a (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 INSERT INTO gtest20a (a) VALUES (10);
@@ -530,6 +540,11 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+-- SET EXPRESSION VIRTUAL | STORED need apply to all inherited tables
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
 \d gtest_parent
 \d gtest_child
 \d gtest_child2
@@ -542,6 +557,11 @@ ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2);
 \d gtest_child
 \d gtest_child2
 \d gtest_child3
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- we leave these tables around for purposes of testing dump/reload/upgrade
 
@@ -566,6 +586,9 @@ ALTER TABLE gtest25 ALTER COLUMN d SET DATA TYPE float8,
   ADD COLUMN y float8 GENERATED ALWAYS AS (d * 4) VIRTUAL;
 SELECT * FROM gtest25 ORDER BY a;
 \d gtest25
+--erorr, can not add and set generation expression in one statement
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
 
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
@@ -625,6 +648,17 @@ INSERT INTO gtest29 (a, b) VALUES (6, 66);
 SELECT * FROM gtest29;
 \d gtest29
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+SELECT * FROM gtest29;
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+SELECT * FROM gtest29;
+
 -- check that dependencies between columns have also been removed
 --ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 --\d gtest29
@@ -648,6 +682,13 @@ ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION;  -- error
 \d gtest30
 \d gtest30_1
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+DEALLOCATE get_generated_info;
 
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') VIRTUAL, c text);
diff --git a/src/test/regress/sql/publication.sql b/src/test/regress/sql/publication.sql
index 00390aecd47..fce608a3e63 100644
--- a/src/test/regress/sql/publication.sql
+++ b/src/test/regress/sql/publication.sql
@@ -549,6 +549,8 @@ ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 
 -- ok: stored generated column "d" can be in the list too
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, d);
+--error
+ALTER TABLE testpub_tbl5 ALTER COLUMN d SET EXPRESSION AS (a + length(b)) VIRTUAL;
 ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 -- error: virtual generated column "e" can't be in list
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, e);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 432509277c9..3f77cee4b23 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1038,6 +1038,7 @@ Gene
 GeneratePruningStepsContext
 GenerationBlock
 GenerationContext
+GenerationExpr
 GenerationPointer
 GenericCosts
 GenericXLogPageData
-- 
2.34.1

From e7a3b3c963cf0ce92b97cd61dc435560820ef311 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Wed, 7 Jan 2026 11:45:37 +0800
Subject: [PATCH v3 1/1] ALTER COLUMN SET EXPRESSION [ VIRTUAL | STORED ]
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

ALTER COLUMN SET EXPRESSION with the VIRTUAL or STORED keyword updates the
generation expression and the column’s persistence simultaneously.

For converting a stored generated column to a virtual one: previously, this
required dropping the column and re-adding it as a virtual generated column,
which would break all the existing dependencies. With this patch, the conversion
can be done directly, making the process more flexible and preserving
dependencies.

For converting a virtual generated column to a stored one: for the same reasons
as above. This will also materializes the values of the virtual generated
column.

context: https://git.postgresql.org/cgit/postgresql.git/commit/?id=83ea6c54025bea67bcd4949a6d58d3fc11c3e21b
discussion: https://postgr.es/m/CACJufxGXLU400QBBgdoboaza0xK58rQqsCAPrxbAMUmo0f8xCQ@mail.gmail.com
---
 doc/src/sgml/ref/alter_table.sgml             |  22 ++-
 src/backend/access/heap/heapam_handler.c      |  12 ++
 src/backend/commands/tablecmds.c              | 142 +++++++++++++++++-
 src/backend/parser/gram.y                     |  28 ++++
 src/include/nodes/parsenodes.h                |  13 ++
 .../test_ddl_deparse/expected/alter_table.out |   6 +
 .../test_ddl_deparse/sql/alter_table.sql      |   2 +
 .../test_ddl_deparse/test_ddl_deparse.c       |  14 +-
 src/test/regress/expected/fast_default.out    |  14 ++
 .../regress/expected/generated_stored.out     | 140 ++++++++++++++++-
 .../regress/expected/generated_virtual.out    | 121 +++++++++++++++
 src/test/regress/expected/publication.out     |   4 +
 src/test/regress/sql/fast_default.sql         |  12 ++
 src/test/regress/sql/generated_stored.sql     |  68 +++++++++
 src/test/regress/sql/generated_virtual.sql    |  43 ++++++
 src/test/regress/sql/publication.sql          |   2 +
 src/tools/pgindent/typedefs.list              |   1 +
 17 files changed, 632 insertions(+), 12 deletions(-)

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 1bd479c917a..cfb3a114fa0 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -52,7 +52,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET DEFAULT <replaceable class="parameter">expression</replaceable>
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP DEFAULT
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET | DROP } NOT NULL
-    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> )
+    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> ) [ STORED | VIRTUAL ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP EXPRESSION [ IF EXISTS ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET GENERATED { ALWAYS | BY DEFAULT } | SET <replaceable>sequence_option</replaceable> | RESTART [ [ WITH ] <replaceable class="parameter">restart</replaceable> ] } [...]
@@ -272,16 +272,26 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry id="sql-altertable-desc-set-expression">
-    <term><literal>SET EXPRESSION AS</literal></term>
+    <term><literal>SET EXPRESSION AS ( <replaceable class="parameter">expression</replaceable> ) [ STORED | VIRTUAL ] </literal></term>
     <listitem>
      <para>
-      This form replaces the expression of a generated column.  Existing data
-      in a stored generated column is rewritten and all the future changes
-      will apply the new generation expression.
+      This form replaces the expression of a generated column and may optionally
+      change its storage persistence type.
+     </para>
+     <para>
+      If the column is stored generated column or <literal>STORED</literal> is
+      specified, existing data is rewritten and all the future changes will apply
+      the new generation expression.
+      If <literal>VIRTUAL</literal> is specified, existing data won’t be rewritten,
+      and <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attgenerated</structfield>
+      is set to <literal>v</literal>.
+      If <literal>STORED</literal> is specified,
+      <link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.<structfield>attgenerated</structfield>
+      set to <literal>s</literal>.
      </para>
 
      <para>
-      When this form is used on a stored generated column, its statistics
+      When this form is used on a stored generated column or <literal>STORED</literal> is specified, its statistics
       are removed, so running
       <link linkend="sql-analyze"><command>ANALYZE</command></link>
       on the table afterwards is recommended.
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index 09a456e9966..2004f2c3b29 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -2375,6 +2375,10 @@ heapam_scan_sample_next_tuple(TableScanDesc scan, SampleScanState *scanstate,
  * currently only known to happen as an after-effect of ALTER TABLE
  * SET WITHOUT OIDS.
  *
+ * 3. ALTER TABLE SET EXPRESSION VIRTUAL will converts the stored generated column
+ *    into virtual; in that case, the corresponding tuple value must
+ *    be set to NULL.
+ *
  * So, we must reconstruct the tuple from component Datums.
  */
 static void
@@ -2394,6 +2398,14 @@ reform_and_rewrite_tuple(HeapTuple tuple,
 	{
 		if (TupleDescCompactAttr(newTupDesc, i)->attisdropped)
 			isnull[i] = true;
+		if (TupleDescCompactAttr(newTupDesc, i)->attgenerated)
+		{
+			if (TupleDescAttr(newTupDesc, i)->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL)
+			{
+				values[i] = (Datum) 0;
+				isnull[i] = true;
+			}
+		}
 	}
 
 	copiedTuple = heap_form_tuple(newTupDesc, values, isnull);
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index f976c0e5c7e..b40019188a5 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -523,6 +523,7 @@ static ObjectAddress ATExecDropIdentity(Relation rel, const char *colName, bool
 static ObjectAddress ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 										 Node *newExpr, LOCKMODE lockmode);
 static void ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode);
+static void ATPrepSetExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode);
 static ObjectAddress ATExecDropExpression(Relation rel, const char *colName, bool missing_ok, LOCKMODE lockmode);
 static ObjectAddress ATExecSetStatistics(Relation rel, const char *colName, int16 colNum,
 										 Node *newValue, LOCKMODE lockmode);
@@ -5032,6 +5033,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			ATSimplePermissions(cmd->subtype, rel,
 								ATT_TABLE | ATT_PARTITIONED_TABLE | ATT_FOREIGN_TABLE);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode, context);
+			ATPrepSetExpression(rel, cmd, recurse, recursing, lockmode);
 			pass = AT_PASS_SET_EXPRESSION;
 			break;
 		case AT_DropExpression: /* ALTER COLUMN DROP EXPRESSION */
@@ -8641,8 +8643,9 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	Expr	   *defval;
 	NewColumnValue *newval;
 	RawColumnDefault *rawEnt;
+	Node	   *raw_default;
 
-	tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
+	tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);
 	if (!HeapTupleIsValid(tuple))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_COLUMN),
@@ -8669,7 +8672,8 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	 * TODO: This could be done, just need to recheck any constraints
 	 * afterwards.
 	 */
-	if (attgenerated == ATTRIBUTE_GENERATED_VIRTUAL &&
+	if (!IsA(newExpr, GenerationExpr) &&
+		attgenerated == ATTRIBUTE_GENERATED_VIRTUAL &&
 		rel->rd_att->constr && rel->rd_att->constr->num_check > 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -8697,7 +8701,80 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 
 	rewrite = (attgenerated == ATTRIBUTE_GENERATED_STORED);
 
-	ReleaseSysCache(tuple);
+	/*
+	 * For ALTER TABLE ALTER COLUMN SET EXPRESSION STORED/VIRTUAL, newExpr is
+	 * a GenerationExpr node. For ALTER TABLE ALTER COLUMN SET EXPRESSION
+	 * without STORED/VIRTUAL, newExpr is a non-GenerationExpr node; see
+	 * gram.y.
+	 */
+	if (!IsA(newExpr, GenerationExpr))
+		raw_default = newExpr;
+	else
+	{
+		GenerationExpr *g = castNode(GenerationExpr, newExpr);
+
+		raw_default = g->raw_expr;
+
+		if (attgenerated == g->generated_kind &&
+			g->generated_kind == ATTRIBUTE_GENERATED_VIRTUAL &&
+			rel->rd_att->constr && rel->rd_att->constr->num_check > 0)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("ALTER TABLE / SET EXPRESSION VIRTUAL is not supported for virtual generated columns in tables with check constraints"),
+					errdetail("Column \"%s\" of relation \"%s\" is a virtual generated column.",
+							  colName, RelationGetRelationName(rel)));
+
+		if (attgenerated != g->generated_kind)
+		{
+			Relation	pg_attribute = table_open(AttributeRelationId,
+												  RowExclusiveLock);
+
+			attgenerated = g->generated_kind;
+			attTup->attgenerated = g->generated_kind;
+
+			if (g->generated_kind == ATTRIBUTE_GENERATED_STORED)
+				rewrite = true;
+			else
+			{
+				char	   *errdetail_msg = NULL;
+
+				RememberAllDependentForRebuilding(tab, AT_SetExpression, rel, attnum, colName);
+
+				/*
+				 * Virtual generated columns do not currently support indexes,
+				 * statistics, user-defined types, or publications.
+				 */
+				if (tab->changedIndexOids != NIL)
+					errdetail_msg = _("Indexes on virtual generated columns are not supported.");
+				else if (tab->changedStatisticsOids != NIL)
+					errdetail_msg = _("Statistics creation on virtual generated columns is not supported.");
+				else if (attTup->atttypid >= FirstUnpinnedObjectId)
+					errdetail_msg = _("Virtual generated columns that make use of user-defined types are not yet supported.");
+				else if (GetRelationPublications(RelationGetRelid(rel)) != NIL)
+					errdetail_msg = _("Publication on virtual generated columns are not supported.");
+
+				if (errdetail_msg != NULL)
+					ereport(ERROR,
+							errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("cannot changed generated column (%s) from %s to %s", colName, "STORED", "VIRTUAL"),
+							errdetail_internal("%s", errdetail_msg));
+
+				/*
+				 * change GENERATED COLUMN from stored to virtual do not need
+				 * table rewrite
+				 */
+				rewrite = false;
+			}
+
+			CatalogTupleUpdate(pg_attribute, &tuple->t_self, tuple);
+
+			InvokeObjectPostAlterHook(RelationRelationId,
+									  RelationGetRelid(rel),
+									  attnum);
+			table_close(pg_attribute, RowExclusiveLock);
+		}
+	}
+	heap_freetuple(tuple);
 
 	if (rewrite)
 	{
@@ -8743,7 +8820,7 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	/* Prepare to store the new expression, in the catalogs */
 	rawEnt = palloc_object(RawColumnDefault);
 	rawEnt->attnum = attnum;
-	rawEnt->raw_default = newExpr;
+	rawEnt->raw_default = raw_default;
 	rawEnt->generated = attgenerated;
 
 	/* Store the generated expression */
@@ -8824,6 +8901,63 @@ ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recurs
 	}
 }
 
+/*
+ * ALTER TABLE ALTER COLUMN SET EXPRESSION [STORED | VIRTUAL]
+ *
+ * This needs to recurse into all child tables; otherwise, the parent and child
+ * may end up with different storage types for the generated column.
+ */
+static void
+ATPrepSetExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode)
+{
+	GenerationExpr *genexpr = NULL;
+
+	if (IsA(cmd->def, GenerationExpr))
+		genexpr = castNode(GenerationExpr, cmd->def);
+
+	/*
+	 * Reject ONLY if there are child tables.
+	 */
+	if (!recurse && !recursing &&
+		genexpr != NULL &&
+		find_inheritance_children(RelationGetRelid(rel), lockmode))
+		ereport(ERROR,
+				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("%s must be applied to child tables too",
+					   (genexpr->generated_kind == ATTRIBUTE_GENERATED_STORED) ?
+					   "ALTER TABLE ... SET EXPRESSION STORED" :
+					   "ALTER TABLE ... SET EXPRESSION VIRTUAL"),
+				errhint("Do not specify the ONLY keyword."));
+
+	/*
+	 * Cannot change generation expression kind from inherited columns.
+	 */
+	if (!recursing && genexpr != NULL)
+	{
+		Form_pg_attribute attTup;
+
+		HeapTuple	tuple = SearchSysCacheAttName(RelationGetRelid(rel), cmd->name);
+
+		if (!HeapTupleIsValid(tuple))
+			ereport(ERROR,
+					errcode(ERRCODE_UNDEFINED_COLUMN),
+					errmsg("column \"%s\" of relation \"%s\" does not exist",
+						   cmd->name, RelationGetRelationName(rel)));
+
+		attTup = (Form_pg_attribute) GETSTRUCT(tuple);
+
+		if (attTup->attinhcount > 0)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("cannot use %s change generation expression from inherited column",
+						   (genexpr->generated_kind == ATTRIBUTE_GENERATED_STORED) ?
+						   "ALTER TABLE ... SET EXPRESSION STORED" :
+						   "ALTER TABLE ... SET EXPRESSION VIRTUAL"));
+
+		ReleaseSysCache(tuple);
+	}
+}
+
 /*
  * Return the address of the affected column.
  */
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 713ee5c10a2..883dccd8e3b 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -2576,6 +2576,34 @@ alter_table_cmd:
 					n->def = $8;
 					$$ = (Node *) n;
 				}
+			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET EXPRESSION AS <expr> VIRTUAL */
+			| ALTER opt_column ColId SET EXPRESSION AS '(' a_expr ')' VIRTUAL
+				{
+					AlterTableCmd *n = makeNode(AlterTableCmd);
+					GenerationExpr *g = makeNode(GenerationExpr);
+
+					g->raw_expr = $8;
+					g->generated_kind = ATTRIBUTE_GENERATED_VIRTUAL;
+
+					n->subtype = AT_SetExpression;
+					n->name = $3;
+					n->def = (Node *) g;
+					$$ = (Node *) n;
+				}
+			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET EXPRESSION AS <expr> STORED */
+			| ALTER opt_column ColId SET EXPRESSION AS '(' a_expr ')' STORED
+				{
+					AlterTableCmd *n = makeNode(AlterTableCmd);
+					GenerationExpr *g = makeNode(GenerationExpr);
+
+					g->raw_expr = $8;
+					g->generated_kind = ATTRIBUTE_GENERATED_STORED;
+
+					n->subtype = AT_SetExpression;
+					n->name = $3;
+					n->def = (Node *) g;
+					$$ = (Node *) n;
+				}
 			/* ALTER TABLE <name> ALTER [COLUMN] <colname> DROP EXPRESSION */
 			| ALTER opt_column ColId DROP EXPRESSION
 				{
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index aac4bfc70d9..8a73b76a7ca 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2906,6 +2906,19 @@ typedef struct Constraint
 	ParseLoc	location;		/* token location, or -1 if unknown */
 } Constraint;
 
+/* ----------------------
+ *	ALTER COLUMN SET EXPRESSION STORED
+ *	ALTER COLUMN SET EXPRESSION VIRTUAL
+ * ----------------------
+ */
+typedef struct GenerationExpr
+{
+	NodeTag		type;
+	Node	   *raw_expr;		/* generation expression as a untransformed
+								 * a_expr node */
+	char		generated_kind; /* STORED or VIRTUAL */
+} GenerationExpr;
+
 /* ----------------------
  *		Create/Drop Table Space Statements
  * ----------------------
diff --git a/src/test/modules/test_ddl_deparse/expected/alter_table.out b/src/test/modules/test_ddl_deparse/expected/alter_table.out
index 3a2f576f3b6..11d000f2f4f 100644
--- a/src/test/modules/test_ddl_deparse/expected/alter_table.out
+++ b/src/test/modules/test_ddl_deparse/expected/alter_table.out
@@ -135,6 +135,12 @@ NOTICE:  DDL test: type simple, tag CREATE TABLE
 ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 3);
 NOTICE:  DDL test: type alter table, tag ALTER TABLE
 NOTICE:    subcommand: type SET EXPRESSION desc column a of table tbl
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) VIRTUAL;
+NOTICE:  DDL test: type alter table, tag ALTER TABLE
+NOTICE:    subcommand: type SET EXPRESSION VIRTUAL desc column a of table tbl
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) STORED;
+NOTICE:  DDL test: type alter table, tag ALTER TABLE
+NOTICE:    subcommand: type SET EXPRESSION STORED desc column a of table tbl
 ALTER TABLE tbl ALTER COLUMN a DROP EXPRESSION;
 NOTICE:  DDL test: type alter table, tag ALTER TABLE
 NOTICE:    subcommand: type DROP EXPRESSION desc column a of table tbl
diff --git a/src/test/modules/test_ddl_deparse/sql/alter_table.sql b/src/test/modules/test_ddl_deparse/sql/alter_table.sql
index 0980097048e..6e65605cf8a 100644
--- a/src/test/modules/test_ddl_deparse/sql/alter_table.sql
+++ b/src/test/modules/test_ddl_deparse/sql/alter_table.sql
@@ -75,6 +75,8 @@ CREATE TABLE tbl (
 );
 
 ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 3);
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) VIRTUAL;
+ALTER TABLE tbl ALTER COLUMN a SET EXPRESSION AS (b::int * 2) STORED;
 ALTER TABLE tbl ALTER COLUMN a DROP EXPRESSION;
 
 ALTER TABLE tbl ALTER COLUMN b SET COMPRESSION pglz;
diff --git a/src/test/modules/test_ddl_deparse/test_ddl_deparse.c b/src/test/modules/test_ddl_deparse/test_ddl_deparse.c
index 380b3e754b7..b9b62341ce5 100644
--- a/src/test/modules/test_ddl_deparse/test_ddl_deparse.c
+++ b/src/test/modules/test_ddl_deparse/test_ddl_deparse.c
@@ -129,8 +129,20 @@ get_altertable_subcmdinfo(PG_FUNCTION_ARGS)
 				strtype = "SET NOT NULL";
 				break;
 			case AT_SetExpression:
-				strtype = "SET EXPRESSION";
+			{
+				if (IsA(subcmd->def, GenerationExpr))
+				{
+					GenerationExpr *genexpr = castNode(GenerationExpr, subcmd->def);
+
+					if (genexpr->generated_kind == ATTRIBUTE_GENERATED_STORED)
+						strtype = "SET EXPRESSION STORED";
+					else
+						strtype = "SET EXPRESSION VIRTUAL";
+				}
+				else
+					strtype = "SET EXPRESSION";
 				break;
+			}
 			case AT_DropExpression:
 				strtype = "DROP EXPRESSION";
 				break;
diff --git a/src/test/regress/expected/fast_default.out b/src/test/regress/expected/fast_default.out
index ccbcdf8403f..4fc5986f9c1 100644
--- a/src/test/regress/expected/fast_default.out
+++ b/src/test/regress/expected/fast_default.out
@@ -70,6 +70,20 @@ NOTICE:  rewriting table has_volatile for reason 4
 -- stored generated columns need a rewrite
 ALTER TABLE has_volatile ADD col7 int GENERATED ALWAYS AS (55) stored;
 NOTICE:  rewriting table has_volatile for reason 2
+-- Changing a generated column from virtual to stored does not require a table
+-- rewrite.
+ALTER TABLE has_volatile ADD col8 int GENERATED ALWAYS AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+NOTICE:  rewriting table has_volatile for reason 2
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+NOTICE:  rewriting table has_volatile for reason 2
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
+NOTICE:  rewriting table has_volatile for reason 2
+-- Changing a generated column from stored to virtual does not require a table
+-- rewrite.
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
 -- Test a large sample of different datatypes
 CREATE TABLE T(pk INT NOT NULL PRIMARY KEY, c_int INT DEFAULT 1);
 SELECT set('t');
diff --git a/src/test/regress/expected/generated_stored.out b/src/test/regress/expected/generated_stored.out
index 8b7a71d8f0c..d8a507668ac 100644
--- a/src/test/regress/expected/generated_stored.out
+++ b/src/test/regress/expected/generated_stored.out
@@ -2,6 +2,12 @@
 CREATE SCHEMA generated_stored_tests;
 GRANT USAGE ON SCHEMA generated_stored_tests TO PUBLIC;
 SET search_path = generated_stored_tests;
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, pg_get_expr(pd.adbin, pa.attrelid)
+FROM    pg_attribute pa JOIN pg_attrdef pd
+ON      pd.adrelid = pa.attrelid
+WHERE   pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0 AND atthasdef
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) STORED);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 SELECT table_name, column_name, column_default, is_nullable, is_generated, generation_expression FROM information_schema.columns WHERE table_schema = 'generated_stored_tests' ORDER BY 1, 2;
@@ -559,6 +565,14 @@ SELECT * FROM gtest_varlena ORDER BY a;
 (2 rows)
 
 DROP TABLE gtest_varlena;
+-- varlena types change from stored to virtual
+CREATE TABLE gtest_varlena (
+    a int,
+    b text STORAGE EXTERNAL GENERATED ALWAYS AS (repeat('g', a)) STORED
+) WITH (autovacuum_enabled = OFF);
+INSERT INTO  gtest_varlena VALUES(2001), (1);
+ALTER TABLE gtest_varlena ALTER COLUMN b SET EXPRESSION AS (repeat('g', a)) VIRTUAL;
+VACUUM (FULL) gtest_varlena; --should ok
 -- composite types
 CREATE TYPE double_int as (a int, b int);
 CREATE TABLE gtest4 (
@@ -573,6 +587,9 @@ SELECT * FROM gtest4;
  6 | (12,18)
 (2 rows)
 
+ALTER TABLE gtest4 ALTER COLUMN b SET EXPRESSION AS ((a * 2, a * 3)) VIRTUAL; --error
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  Virtual generated columns that make use of user-defined types are not yet supported.
 DROP TABLE gtest4;
 DROP TYPE double_int;
 -- using tableoid is allowed
@@ -666,6 +683,10 @@ ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated b
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 50); -- fails on existing row
 ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated by some row
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 61); -- ok
+ALTER TABLE gtest20a ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL; -- violates constraint
+ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated by some row
+ALTER TABLE gtest20a ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED; -- violates constraint
+ERROR:  check constraint "gtest20a_b_check" of relation "gtest20a" is violated by some row
 CREATE TABLE gtest20b (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 INSERT INTO gtest20b (a) VALUES (10);
 INSERT INTO gtest20b (a) VALUES (30);
@@ -833,6 +854,9 @@ ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 5); -- error
 ERROR:  insert or update on table "gtest23b" violates foreign key constraint "gtest23b_b_fkey"
 DETAIL:  Key (b)=(5) is not present in table "gtest23a".
 ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 1); -- ok
+--virutal generated column does not support foreign key
+ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 11) VIRTUAL; --error
+ERROR:  foreign key constraints on virtual generated columns are not supported
 DROP TABLE gtest23b;
 DROP TABLE gtest23a;
 CREATE TABLE gtest23p (x int, y int GENERATED ALWAYS AS (x * 2) STORED, PRIMARY KEY (y));
@@ -858,6 +882,10 @@ CREATE TABLE gtest24nn (a int, b gtestdomainnn GENERATED ALWAYS AS (a * 2) STORE
 INSERT INTO gtest24nn (a) VALUES (4);  -- ok
 INSERT INTO gtest24nn (a) VALUES (NULL);  -- error
 ERROR:  value for domain gtestdomainnn violates check constraint "gtestdomainnn_check"
+--error, virutal generated column does not support domains
+ALTER TABLE gtest24nn ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  Virtual generated columns that make use of user-defined types are not yet supported.
 -- typed tables (currently not supported)
 CREATE TYPE gtest_type AS (f1 integer, f2 text, f3 bigint);
 CREATE TABLE gtest28 OF gtest_type (f1 WITH OPTIONS GENERATED ALWAYS AS (f2 *2) STORED);
@@ -980,7 +1008,17 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION STORED must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION VIRTUAL must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
 \d gtest_parent
            Partitioned table "generated_stored_tests.gtest_parent"
  Column |  Type  | Collation | Nullable |               Default               
@@ -1065,6 +1103,26 @@ Partition of: gtest_parent FOR VALUES FROM ('08-01-2016') TO ('09-01-2016')
  f3     | bigint |           |          | generated always as (f2 * 2) stored
 Partition of: gtest_parent FOR VALUES FROM ('09-01-2016') TO ('10-01-2016')
 
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | pg_get_expr 
+--------------+---------+--------+--------------+-------------
+ gtest_child  | f3      |      3 | v            | (f2 * 11)
+ gtest_child2 | f3      |      3 | v            | (f2 * 11)
+ gtest_child3 | f3      |      3 | v            | (f2 * 11)
+ gtest_parent | f3      |      3 | v            | (f2 * 11)
+(4 rows)
+
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | pg_get_expr 
+--------------+---------+--------+--------------+-------------
+ gtest_child  | f3      |      3 | s            | (f2 * 2)
+ gtest_child2 | f3      |      3 | s            | (f2 * 2)
+ gtest_child3 | f3      |      3 | s            | (f2 * 2)
+ gtest_parent | f3      |      3 | s            | (f2 * 2)
+(4 rows)
+
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
    tableoid   |     f1     | f2 | f3 
 --------------+------------+----+----
@@ -1141,6 +1199,10 @@ SELECT * FROM gtest25 ORDER BY a;
 Indexes:
     "gtest25_pkey" PRIMARY KEY, btree (a)
 
+--error: adding a column and setting its generation expression cannot be done in a single statement.
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
+ERROR:  column "d1" of relation "gtest25" does not exist
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
     a int,
@@ -1279,6 +1341,46 @@ ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 --------+---------+-----------+----------+---------
  b      | integer |           |          | 
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+DROP TABLE gtest29;
+CREATE TABLE gtest29 (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
+INSERT INTO gtest29 (a) VALUES (3), (4);
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | pg_get_expr 
+---------+---------+--------+--------------+-------------
+ gtest29 | b       |      2 | v            | (a * 3)
+(1 row)
+
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  9
+ 4 | 12
+(2 rows)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 4);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | pg_get_expr 
+---------+---------+--------+--------------+-------------
+ gtest29 | b       |      2 | v            | (a * 4)
+(1 row)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 5) STORED;
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 | 15
+ 4 | 20
+(2 rows)
+
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | pg_get_expr 
+---------+---------+--------+--------------+-------------
+ gtest29 | b       |      2 | s            | (a * 5)
+(1 row)
+
 -- with inheritance
 CREATE TABLE gtest30 (
     a int,
@@ -1329,6 +1431,27 @@ Inherits: gtest30
 
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
 ERROR:  cannot drop generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | pg_get_expr 
+-----------+---------+--------+--------------+-------------
+ gtest30   | b       |      2 | s            | (a * 2)
+ gtest30_1 | b       |      2 | s            | (a * 2)
+(2 rows)
+
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | pg_get_expr 
+-----------+---------+--------+--------------+-------------
+ gtest30   | b       |      2 | v            | (a * 2)
+ gtest30_1 | b       |      2 | v            | (a * 2)
+(2 rows)
+
+DEALLOCATE get_generated_info;
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
@@ -1338,15 +1461,30 @@ ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row
 ALTER TABLE gtest31_2 ADD CONSTRAINT cc CHECK ((y).b IS NOT NULL);
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1');
 ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row type
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') STORED;
+ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row type
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') VIRTUAL;
 ALTER TABLE gtest31_2 DROP CONSTRAINT cc;
 CREATE STATISTICS gtest31_2_stat ON ((y).b is not null) FROM gtest31_2;
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2');
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2') STORED;
 ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row type
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2') VIRTUAL;
 DROP STATISTICS gtest31_2_stat;
 CREATE INDEX gtest31_2_y_idx ON gtest31_2(((y).b));
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello3');
-ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row type
 DROP TABLE gtest31_1, gtest31_2;
+CREATE TABLE gtest31_1 (a int, b int GENERATED ALWAYS AS (a) STORED);
+CREATE STATISTICS gtest31_1_stat ON (b is not null) FROM gtest31_1;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  Statistics creation on virtual generated columns is not supported.
+DROP STATISTICS gtest31_1_stat;
+CREATE INDEX ON gtest31_1(b);
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+ERROR:  cannot changed generated column (b) from STORED to VIRTUAL
+DETAIL:  Indexes on virtual generated columns are not supported.
+DROP TABLE gtest31_1;
 -- Check it for a partitioned table, too
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text) PARTITION BY LIST (a);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
diff --git a/src/test/regress/expected/generated_virtual.out b/src/test/regress/expected/generated_virtual.out
index 249e68be654..68ffc938665 100644
--- a/src/test/regress/expected/generated_virtual.out
+++ b/src/test/regress/expected/generated_virtual.out
@@ -2,6 +2,12 @@
 CREATE SCHEMA generated_virtual_tests;
 GRANT USAGE ON SCHEMA generated_virtual_tests TO PUBLIC;
 SET search_path = generated_virtual_tests;
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, pg_get_expr(pd.adbin, pa.attrelid)
+FROM    pg_attribute pa JOIN pg_attrdef pd
+ON      pd.adrelid = pa.attrelid
+WHERE   pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0 AND atthasdef
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) VIRTUAL);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 SELECT table_name, column_name, column_default, is_nullable, is_generated, generation_expression FROM information_schema.columns WHERE table_schema = 'generated_virtual_tests' ORDER BY 1, 2;
@@ -645,6 +651,23 @@ DETAIL:  Column "b" of relation "gtest20" is a virtual generated column.
 ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3);  -- ok (currently not supported)
 ERROR:  ALTER TABLE / SET EXPRESSION is not supported for virtual generated columns in tables with check constraints
 DETAIL:  Column "b" of relation "gtest20" is a virtual generated column.
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;  -- ok (currently not supported)
+ERROR:  ALTER TABLE / SET EXPRESSION VIRTUAL is not supported for virtual generated columns in tables with check constraints
+DETAIL:  Column "b" of relation "gtest20" is a virtual generated column.
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 5) STORED;  --error, violates constraint
+ERROR:  check constraint "gtest20_b_check" of relation "gtest20" is violated by some row
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;  --ok
+\d gtest20
+                   Table "generated_virtual_tests.gtest20"
+ Column |  Type   | Collation | Nullable |              Default               
+--------+---------+-----------+----------+------------------------------------
+ a      | integer |           | not null | 
+ b      | integer |           |          | generated always as (a * 3) stored
+Indexes:
+    "gtest20_pkey" PRIMARY KEY, btree (a)
+Check constraints:
+    "gtest20_b_check" CHECK (b < 50)
+
 CREATE TABLE gtest20a (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 INSERT INTO gtest20a (a) VALUES (10);
 INSERT INTO gtest20a (a) VALUES (30);
@@ -943,6 +966,17 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+-- ALTER COLUMN SET EXPRESSION VIRTUAL/STORED must apply to all inherited tables
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION STORED must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
+ERROR:  ALTER TABLE ... SET EXPRESSION VIRTUAL must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
 \d gtest_parent
        Partitioned table "generated_virtual_tests.gtest_parent"
  Column |  Type  | Collation | Nullable |           Default            
@@ -1027,6 +1061,26 @@ Partition of: gtest_parent FOR VALUES FROM ('08-01-2016') TO ('09-01-2016')
  f3     | bigint |           |          | generated always as (f2 * 2)
 Partition of: gtest_parent FOR VALUES FROM ('09-01-2016') TO ('10-01-2016')
 
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | pg_get_expr 
+--------------+---------+--------+--------------+-------------
+ gtest_child  | f3      |      3 | s            | (f2 * 11)
+ gtest_child2 | f3      |      3 | s            | (f2 * 11)
+ gtest_child3 | f3      |      3 | s            | (f2 * 11)
+ gtest_parent | f3      |      3 | s            | (f2 * 11)
+(4 rows)
+
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+    table     | attname | attnum | attgenerated | pg_get_expr 
+--------------+---------+--------+--------------+-------------
+ gtest_child  | f3      |      3 | v            | (f2 * 2)
+ gtest_child2 | f3      |      3 | v            | (f2 * 2)
+ gtest_child3 | f3      |      3 | v            | (f2 * 2)
+ gtest_parent | f3      |      3 | v            | (f2 * 2)
+(4 rows)
+
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
    tableoid   |     f1     | f2 | f3 
 --------------+------------+----+----
@@ -1103,6 +1157,10 @@ SELECT * FROM gtest25 ORDER BY a;
 Indexes:
     "gtest25_pkey" PRIMARY KEY, btree (a)
 
+--error, can not add and set generation expression in one statement
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
+ERROR:  column "d1" of relation "gtest25" does not exist
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
     a int,
@@ -1244,6 +1302,45 @@ SELECT * FROM gtest29;
  a      | integer |           |          | 
  b      | integer |           |          | generated always as (a * 3)
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | pg_get_expr 
+---------+---------+--------+--------------+-------------
+ gtest29 | b       |      2 | s            | (a * 2)
+(1 row)
+
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  6
+ 4 |  8
+ 5 | 10
+(3 rows)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 4);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | pg_get_expr 
+---------+---------+--------+--------------+-------------
+ gtest29 | b       |      2 | s            | (a * 4)
+(1 row)
+
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+  table  | attname | attnum | attgenerated | pg_get_expr 
+---------+---------+--------+--------------+-------------
+ gtest29 | b       |      2 | v            | (a * 3)
+(1 row)
+
+SELECT * FROM gtest29;
+ a | b  
+---+----
+ 3 |  9
+ 4 | 12
+ 5 | 15
+(3 rows)
+
 -- check that dependencies between columns have also been removed
 --ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 --\d gtest29
@@ -1299,6 +1396,27 @@ Inherits: gtest30
 
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
 ERROR:  cannot drop generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION STORED change generation expression from inherited column
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ERROR:  cannot use ALTER TABLE ... SET EXPRESSION VIRTUAL change generation expression from inherited column
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | pg_get_expr 
+-----------+---------+--------+--------------+-------------
+ gtest30   | b       |      2 | s            | (a * 2)
+ gtest30_1 | b       |      2 | s            | (a * 2)
+(2 rows)
+
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+   table   | attname | attnum | attgenerated | pg_get_expr 
+-----------+---------+--------+--------------+-------------
+ gtest30   | b       |      2 | v            | (a * 3)
+ gtest30_1 | b       |      2 | v            | (a * 3)
+(2 rows)
+
+DEALLOCATE get_generated_info;
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') VIRTUAL, c text);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
@@ -1307,6 +1425,9 @@ ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row
 -- bug #18970
 ALTER TABLE gtest31_2 ADD CONSTRAINT cc CHECK ((y).b IS NOT NULL);
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1');
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') VIRTUAL;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') STORED;
+ERROR:  cannot alter table "gtest31_1" because column "gtest31_2.y" uses its row type
 ALTER TABLE gtest31_2 DROP CONSTRAINT cc;
 CREATE STATISTICS gtest31_2_stat ON ((y).b is not null) FROM gtest31_2;
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2');
diff --git a/src/test/regress/expected/publication.out b/src/test/regress/expected/publication.out
index 7fb49aaf29b..2e7e2bc7af2 100644
--- a/src/test/regress/expected/publication.out
+++ b/src/test/regress/expected/publication.out
@@ -876,6 +876,10 @@ DETAIL:  Column list used by the publication does not cover the replica identity
 ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 -- ok: stored generated column "d" can be in the list too
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, d);
+--error
+ALTER TABLE testpub_tbl5 ALTER COLUMN d SET EXPRESSION AS (a + length(b)) VIRTUAL;
+ERROR:  cannot changed generated column (d) from STORED to VIRTUAL
+DETAIL:  Publication on virtual generated columns are not supported.
 ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 -- error: virtual generated column "e" can't be in list
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, e);
diff --git a/src/test/regress/sql/fast_default.sql b/src/test/regress/sql/fast_default.sql
index 068dd0bc8aa..6e215550434 100644
--- a/src/test/regress/sql/fast_default.sql
+++ b/src/test/regress/sql/fast_default.sql
@@ -77,6 +77,18 @@ ALTER TABLE has_volatile ALTER COLUMN col1 SET DATA TYPE float8,
 -- stored generated columns need a rewrite
 ALTER TABLE has_volatile ADD col7 int GENERATED ALWAYS AS (55) stored;
 
+-- Changing a generated column from virtual to stored does not require a table
+-- rewrite.
+ALTER TABLE has_volatile ADD col8 int GENERATED ALWAYS AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) STORED;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
+
+-- Changing a generated column from stored to virtual does not require a table
+-- rewrite.
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55) VIRTUAL;
+ALTER TABLE has_volatile ALTER COLUMN col8 SET EXPRESSION AS (55);
 
 
 -- Test a large sample of different datatypes
diff --git a/src/test/regress/sql/generated_stored.sql b/src/test/regress/sql/generated_stored.sql
index 2001a47bcc6..dfbea1a66b7 100644
--- a/src/test/regress/sql/generated_stored.sql
+++ b/src/test/regress/sql/generated_stored.sql
@@ -5,6 +5,13 @@ CREATE SCHEMA generated_stored_tests;
 GRANT USAGE ON SCHEMA generated_stored_tests TO PUBLIC;
 SET search_path = generated_stored_tests;
 
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, pg_get_expr(pd.adbin, pa.attrelid)
+FROM    pg_attribute pa JOIN pg_attrdef pd
+ON      pd.adrelid = pa.attrelid
+WHERE   pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0 AND atthasdef
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
+
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) STORED);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 
@@ -251,6 +258,15 @@ INSERT INTO gtest_varlena (a) VALUES(NULL);
 SELECT * FROM gtest_varlena ORDER BY a;
 DROP TABLE gtest_varlena;
 
+-- varlena types change from stored to virtual
+CREATE TABLE gtest_varlena (
+    a int,
+    b text STORAGE EXTERNAL GENERATED ALWAYS AS (repeat('g', a)) STORED
+) WITH (autovacuum_enabled = OFF);
+INSERT INTO  gtest_varlena VALUES(2001), (1);
+ALTER TABLE gtest_varlena ALTER COLUMN b SET EXPRESSION AS (repeat('g', a)) VIRTUAL;
+VACUUM (FULL) gtest_varlena; --should ok
+
 -- composite types
 CREATE TYPE double_int as (a int, b int);
 CREATE TABLE gtest4 (
@@ -259,6 +275,7 @@ CREATE TABLE gtest4 (
 );
 INSERT INTO gtest4 VALUES (1), (6);
 SELECT * FROM gtest4;
+ALTER TABLE gtest4 ALTER COLUMN b SET EXPRESSION AS ((a * 2, a * 3)) VIRTUAL; --error
 
 DROP TABLE gtest4;
 DROP TYPE double_int;
@@ -326,6 +343,8 @@ ALTER TABLE gtest20a ADD CHECK (b < 50);  -- fails on existing row
 -- table rewrite cases
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 50); -- fails on existing row
 ALTER TABLE gtest20a ADD COLUMN c float8 DEFAULT random() CHECK (b < 61); -- ok
+ALTER TABLE gtest20a ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL; -- violates constraint
+ALTER TABLE gtest20a ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED; -- violates constraint
 
 CREATE TABLE gtest20b (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED);
 INSERT INTO gtest20b (a) VALUES (10);
@@ -403,6 +422,8 @@ INSERT INTO gtest23b VALUES (5);  -- error
 ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 5); -- error
 ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 1); -- ok
 
+--virutal generated column does not support foreign key
+ALTER TABLE gtest23b ALTER COLUMN b SET EXPRESSION AS (a * 11) VIRTUAL; --error
 DROP TABLE gtest23b;
 DROP TABLE gtest23a;
 
@@ -428,6 +449,9 @@ CREATE TABLE gtest24nn (a int, b gtestdomainnn GENERATED ALWAYS AS (a * 2) STORE
 INSERT INTO gtest24nn (a) VALUES (4);  -- ok
 INSERT INTO gtest24nn (a) VALUES (NULL);  -- error
 
+--error, virutal generated column does not support domains
+ALTER TABLE gtest24nn ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+
 -- typed tables (currently not supported)
 CREATE TYPE gtest_type AS (f1 integer, f2 text, f3 bigint);
 CREATE TABLE gtest28 OF gtest_type (f1 WITH OPTIONS GENERATED ALWAYS AS (f2 *2) STORED);
@@ -486,7 +510,11 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
 \d gtest_parent
 \d gtest_child
 \d gtest_child2
@@ -499,6 +527,10 @@ ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2);
 \d gtest_child
 \d gtest_child2
 \d gtest_child3
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- we leave these tables around for purposes of testing dump/reload/upgrade
 
@@ -523,6 +555,9 @@ ALTER TABLE gtest25 ALTER COLUMN d SET DATA TYPE float8,
   ADD COLUMN y float8 GENERATED ALWAYS AS (d * 4) STORED;
 SELECT * FROM gtest25 ORDER BY a;
 \d gtest25
+--error: adding a column and setting its generation expression cannot be done in a single statement.
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
 
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
@@ -578,6 +613,20 @@ SELECT * FROM gtest29;
 ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 \d gtest29
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+DROP TABLE gtest29;
+CREATE TABLE gtest29 (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
+INSERT INTO gtest29 (a) VALUES (3), (4);
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+SELECT * FROM gtest29;
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 4);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 5) STORED;
+SELECT * FROM gtest29;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+
 -- with inheritance
 CREATE TABLE gtest30 (
     a int,
@@ -597,6 +646,13 @@ ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION;  -- error
 \d gtest30
 \d gtest30_1
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+DEALLOCATE get_generated_info;
 
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text);
@@ -606,10 +662,14 @@ ALTER TABLE gtest31_1 ALTER COLUMN b TYPE varchar;  -- fails
 -- bug #18970: these cases are unsupported, but make sure they fail cleanly
 ALTER TABLE gtest31_2 ADD CONSTRAINT cc CHECK ((y).b IS NOT NULL);
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1');
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') STORED;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') VIRTUAL;
 ALTER TABLE gtest31_2 DROP CONSTRAINT cc;
 
 CREATE STATISTICS gtest31_2_stat ON ((y).b is not null) FROM gtest31_2;
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2');
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2') STORED;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello2') VIRTUAL;
 DROP STATISTICS gtest31_2_stat;
 
 CREATE INDEX gtest31_2_y_idx ON gtest31_2(((y).b));
@@ -617,6 +677,14 @@ ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello3');
 
 DROP TABLE gtest31_1, gtest31_2;
 
+CREATE TABLE gtest31_1 (a int, b int GENERATED ALWAYS AS (a) STORED);
+CREATE STATISTICS gtest31_1_stat ON (b is not null) FROM gtest31_1;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+DROP STATISTICS gtest31_1_stat;
+CREATE INDEX ON gtest31_1(b);
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS (a) VIRTUAL; --error
+DROP TABLE gtest31_1;
+
 -- Check it for a partitioned table, too
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') STORED, c text) PARTITION BY LIST (a);
 CREATE TABLE gtest31_2 (x int, y gtest31_1);
diff --git a/src/test/regress/sql/generated_virtual.sql b/src/test/regress/sql/generated_virtual.sql
index 81152b39a79..1782558fd7f 100644
--- a/src/test/regress/sql/generated_virtual.sql
+++ b/src/test/regress/sql/generated_virtual.sql
@@ -5,6 +5,13 @@ CREATE SCHEMA generated_virtual_tests;
 GRANT USAGE ON SCHEMA generated_virtual_tests TO PUBLIC;
 SET search_path = generated_virtual_tests;
 
+PREPARE get_generated_info(regclass[], text[]) AS
+SELECT attrelid::regclass as table, attname, attnum, attgenerated, pg_get_expr(pd.adbin, pa.attrelid)
+FROM    pg_attribute pa JOIN pg_attrdef pd
+ON      pd.adrelid = pa.attrelid
+WHERE   pa.attrelid = ANY($1) AND pa.attname =ANY($2) AND pa.attnum > 0 AND atthasdef
+ORDER BY attrelid::regclass::text COLLATE "C", attnum;
+
 CREATE TABLE gtest0 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (55) VIRTUAL);
 CREATE TABLE gtest1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 
@@ -319,6 +326,10 @@ INSERT INTO gtest20 (a) VALUES (30);  -- violates constraint
 
 ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 100);  -- violates constraint (currently not supported)
 ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3);  -- ok (currently not supported)
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;  -- ok (currently not supported)
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 5) STORED;  --error, violates constraint
+ALTER TABLE gtest20 ALTER COLUMN b SET EXPRESSION AS (a * 3) STORED;  --ok
+\d gtest20
 
 CREATE TABLE gtest20a (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) VIRTUAL);
 INSERT INTO gtest20a (a) VALUES (10);
@@ -530,6 +541,11 @@ SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- alter only parent's and one child's generation expression
 ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4);
 ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10);
+-- ALTER COLUMN SET EXPRESSION VIRTUAL/STORED must apply to all inherited tables
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) STORED; --error
+ALTER TABLE ONLY gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 4) VIRTUAL; --error
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) VIRTUAL; --error
+ALTER TABLE gtest_child ALTER COLUMN f3 SET EXPRESSION AS (f2 * 10) STORED; --error
 \d gtest_parent
 \d gtest_child
 \d gtest_child2
@@ -542,6 +558,10 @@ ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2);
 \d gtest_child
 \d gtest_child2
 \d gtest_child3
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 11) STORED;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
+ALTER TABLE gtest_parent ALTER COLUMN f3 SET EXPRESSION AS (f2 * 2) VIRTUAL;
+EXECUTE get_generated_info('{gtest_parent, gtest_child, gtest_child2, gtest_child3}', '{f3}');
 SELECT tableoid::regclass, * FROM gtest_parent ORDER BY 1, 2, 3;
 -- we leave these tables around for purposes of testing dump/reload/upgrade
 
@@ -566,6 +586,9 @@ ALTER TABLE gtest25 ALTER COLUMN d SET DATA TYPE float8,
   ADD COLUMN y float8 GENERATED ALWAYS AS (d * 4) VIRTUAL;
 SELECT * FROM gtest25 ORDER BY a;
 \d gtest25
+--error, can not add and set generation expression in one statement
+ALTER TABLE gtest25 ADD COLUMN d1 int GENERATED ALWAYS AS (a * 2) VIRTUAL,
+  ALTER COLUMN d1 SET EXPRESSION AS (a * 3) STORED;
 
 -- ALTER TABLE ... ALTER COLUMN
 CREATE TABLE gtest27 (
@@ -625,6 +648,17 @@ INSERT INTO gtest29 (a, b) VALUES (6, 66);
 SELECT * FROM gtest29;
 \d gtest29
 
+-- ALTER COLUMN ... SET EXPRESSION VIRTUAL
+-- ALTER COLUMN ... SET EXPRESSION STORED
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+SELECT * FROM gtest29;
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 4);
+EXECUTE get_generated_info('{gtest29}', '{b}');
+ALTER TABLE gtest29 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest29}', '{b}');
+SELECT * FROM gtest29;
+
 -- check that dependencies between columns have also been removed
 --ALTER TABLE gtest29 DROP COLUMN a;  -- should not drop b
 --\d gtest29
@@ -648,6 +682,13 @@ ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION;  -- error
 \d gtest30
 \d gtest30_1
 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;  -- error
+ALTER TABLE gtest30_1 ALTER COLUMN b SET EXPRESSION AS (a * 2) VIRTUAL;  -- error
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 2) STORED;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+ALTER TABLE gtest30 ALTER COLUMN b SET EXPRESSION AS (a * 3) VIRTUAL;
+EXECUTE get_generated_info('{gtest30, gtest30_1}', '{b}');
+DEALLOCATE get_generated_info;
 
 -- composite type dependencies
 CREATE TABLE gtest31_1 (a int, b text GENERATED ALWAYS AS ('hello') VIRTUAL, c text);
@@ -657,6 +698,8 @@ ALTER TABLE gtest31_1 ALTER COLUMN b TYPE varchar;  -- fails
 -- bug #18970
 ALTER TABLE gtest31_2 ADD CONSTRAINT cc CHECK ((y).b IS NOT NULL);
 ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1');
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') VIRTUAL;
+ALTER TABLE gtest31_1 ALTER COLUMN b SET EXPRESSION AS ('hello1') STORED;
 ALTER TABLE gtest31_2 DROP CONSTRAINT cc;
 
 CREATE STATISTICS gtest31_2_stat ON ((y).b is not null) FROM gtest31_2;
diff --git a/src/test/regress/sql/publication.sql b/src/test/regress/sql/publication.sql
index 85b00bd67c8..0ef62d4ad66 100644
--- a/src/test/regress/sql/publication.sql
+++ b/src/test/regress/sql/publication.sql
@@ -547,6 +547,8 @@ ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 
 -- ok: stored generated column "d" can be in the list too
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, d);
+--error
+ALTER TABLE testpub_tbl5 ALTER COLUMN d SET EXPRESSION AS (a + length(b)) VIRTUAL;
 ALTER PUBLICATION testpub_fortable DROP TABLE testpub_tbl5;
 -- error: virtual generated column "e" can't be in list
 ALTER PUBLICATION testpub_fortable ADD TABLE testpub_tbl5 (a, e);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index b9e671fcda8..16348426f5e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -1049,6 +1049,7 @@ Gene
 GeneratePruningStepsContext
 GenerationBlock
 GenerationContext
+GenerationExpr
 GenerationPointer
 GenericCosts
 GenericXLogPageData
-- 
2.34.1