fix NOT VALID NOT NULL with ALTER COLUMN SET IDENTITY

From 32dc89c57e47a89d8a0719a690f70a089d738925 Mon Sep 17 00:00:00 2001
From: jian he <jian.universality@gmail.com>
Date: Wed, 3 Sep 2025 16:27:24 +0800
Subject: [PATCH v1 1/1] fix NOT VALID NOT NULL CONSTRAINT with identity column

fix the below problem:

CREATE TABLE notnull_tbl1 (a int, b int);
INSERT INTO notnull_tbl1 VALUES (NULL, 1), (300, 3);
ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn NOT NULL a NOT VALID; -- ok

ALTER TABLE notnull_tbl1 ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY; --expect error
ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn NOT NULL a NOT VALID,
  ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY; --expect error
---
 src/backend/commands/tablecmds.c          | 20 ++++++++++++++++++++
 src/test/regress/expected/constraints.out | 11 +++++++++++
 src/test/regress/sql/constraints.sql      |  6 ++++++
 3 files changed, 37 insertions(+)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 082a3575d62..b9f1ae6788f 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8277,6 +8277,26 @@ ATExecAddIdentity(Relation rel, const char *colName,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("column \"%s\" of relation \"%s\" must be declared NOT NULL before identity can be added",
 						colName, RelationGetRelationName(rel))));
+	else
+	{
+		HeapTuple	contup;
+		Form_pg_constraint conForm;
+
+		contup = findNotNullConstraintAttnum(RelationGetRelid(rel),
+											 attnum);
+		if (!HeapTupleIsValid(contup))
+			elog(ERROR, "cache lookup failed for not-null constraint on column \"%s\" of relation \"%s\"",
+						 colName, RelationGetRelationName(rel));
+
+		conForm = (Form_pg_constraint) GETSTRUCT(contup);
+		if (!conForm->convalidated)
+			ereport(ERROR,
+					errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					errmsg("incompatible NOT VALID constraint \"%s\" on relation \"%s\"",
+						   NameStr(conForm->conname), RelationGetRelationName(rel)),
+					errhint("You might need to validate it using %s.",
+							"ALTER TABLE ... VALIDATE CONSTRAINT"));
+	}
 
 	if (attTup->attidentity)
 		ereport(ERROR,
diff --git a/src/test/regress/expected/constraints.out b/src/test/regress/expected/constraints.out
index 3590d3274f0..af448eb9b3b 100644
--- a/src/test/regress/expected/constraints.out
+++ b/src/test/regress/expected/constraints.out
@@ -1404,6 +1404,17 @@ ALTER TABLE notnull_tbl1 ADD PRIMARY KEY (a);
 ERROR:  cannot create primary key on column "a"
 DETAIL:  The constraint "nn" on column "a" of table "notnull_tbl1", marked NOT VALID, is incompatible with a primary key.
 HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
+-- cannot set column set identity with an invalid not-null
+ALTER TABLE notnull_tbl1 ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY;
+ERROR:  incompatible NOT VALID constraint "nn" on relation "notnull_tbl1"
+HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
+ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn NOT NULL a NOT VALID, ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY;
+ERROR:  incompatible NOT VALID constraint "nn" on relation "notnull_tbl1"
+HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
+-- cannot set column as serial with a no inherit not-null
+ALTER TABLE notnull_tbl1 ADD COLUMN d serial, ADD CONSTRAINT nn NOT NULL d NO INHERIT;
+ERROR:  cannot change NO INHERIT status of NOT NULL constraint "notnull_tbl1_d_not_null" on relation "notnull_tbl1"
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 -- ALTER column SET NOT NULL validates an invalid constraint (but this fails
 -- because of rows with null values)
 ALTER TABLE notnull_tbl1 ALTER a SET NOT NULL;
diff --git a/src/test/regress/sql/constraints.sql b/src/test/regress/sql/constraints.sql
index 1f6dc8fd69f..d31dae0b68e 100644
--- a/src/test/regress/sql/constraints.sql
+++ b/src/test/regress/sql/constraints.sql
@@ -831,6 +831,12 @@ ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn NOT NULL a;
 
 -- cannot add primary key on a column with an invalid not-null
 ALTER TABLE notnull_tbl1 ADD PRIMARY KEY (a);
+-- cannot set column set identity with an invalid not-null
+ALTER TABLE notnull_tbl1 ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY;
+ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn NOT NULL a NOT VALID, ALTER COLUMN a ADD GENERATED ALWAYS AS IDENTITY;
+
+-- cannot set column as serial with a no inherit not-null
+ALTER TABLE notnull_tbl1 ADD COLUMN d serial, ADD CONSTRAINT nn NOT NULL d NO INHERIT;
 
 -- ALTER column SET NOT NULL validates an invalid constraint (but this fails
 -- because of rows with null values)
-- 
2.34.1