Fix error message for ALTER CONSTRAINT ... NOT VALID

Álvaro Herrera · jianhe-fun · Fujii Masao · Álvaro Herrera · commit c989affb527d · 2025-07-02T17:02:27.000+02:00
Trying to alter a constraint so that it becomes NOT VALID results in an error that assumes the constraint is a foreign key. This is potentially wrong, so give a more generic error message. While at it, give CREATE CONSTRAINT TRIGGER a better error message as well. Co-authored-by: jian he <jian.universality@gmail.com> Co-authored-by: Fujii Masao <masao.fujii@oss.nttdata.com> Co-authored-by: Álvaro Herrera <alvherre@kurilemu.de> Co-authored-by: Amul Sul <sulamul@gmail.com> Discussion: https://postgr.es/m/CACJufxHSp2puxP=q8ZtUGL1F+heapnzqFBZy5ZNGUjUgwjBqTQ@mail.gmail.com
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
@@ -2668,6 +2668,12 @@ alter_table_cmd:
 						c->alterDeferrability = true;
 					if ($4 & CAS_NO_INHERIT)
 						c->alterInheritability = true;
+					/* handle unsupported case with specific error message */
+					if ($4 & CAS_NOT_VALID)
+						ereport(ERROR,
+								errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								errmsg("constraints cannot be altered to be NOT VALID"),
+								parser_errposition(@4));
 					processCASbits($4, @4, "FOREIGN KEY",
 									&c->deferrable,
 									&c->initdeferred,
diff --git a/src/test/regress/expected/constraints.out b/src/test/regress/expected/constraints.out
@@ -748,6 +748,11 @@ ALTER TABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key ENFORCED;
 ERROR:  cannot alter enforceability of constraint "unique_tbl_i_key" of relation "unique_tbl"
 ALTER TABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key NOT ENFORCED;
 ERROR:  cannot alter enforceability of constraint "unique_tbl_i_key" of relation "unique_tbl"
+-- can't make an existing constraint NOT VALID
+ALTER TABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key NOT VALID;
+ERROR:  constraints cannot be altered to be NOT VALID
+LINE 1: ...ABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key NOT VALID;
+                                                             ^
 DROP TABLE unique_tbl;
 --
 -- EXCLUDE constraints
diff --git a/src/test/regress/expected/foreign_key.out b/src/test/regress/expected/foreign_key.out
@@ -1359,7 +1359,7 @@ LINE 1: ...e ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY ...
 ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NO INHERIT;
 ERROR:  constraint "fktable_fk_fkey" of relation "fktable" is not a not-null constraint
 ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT VALID;
-ERROR:  FOREIGN KEY constraints cannot be marked NOT VALID
+ERROR:  constraints cannot be altered to be NOT VALID
 LINE 1: ...ER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT VALID;
                                                              ^
 ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey ENFORCED NOT ENFORCED;
diff --git a/src/test/regress/sql/constraints.sql b/src/test/regress/sql/constraints.sql
@@ -537,6 +537,9 @@ CREATE TABLE UNIQUE_NOTEN_TBL(i int UNIQUE NOT ENFORCED);
 ALTER TABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key ENFORCED;
 ALTER TABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key NOT ENFORCED;
 
+-- can't make an existing constraint NOT VALID
+ALTER TABLE unique_tbl ALTER CONSTRAINT unique_tbl_i_key NOT VALID;
+
 DROP TABLE unique_tbl;
 
 --

Original file line number	Diff line number	Diff line change
`@@ -1359,7 +1359,7 @@ LINE 1: ...e ALTER CONSTRAINT fktable_fk_fkey NOT DEFERRABLE INITIALLY ...`
`1359`	`1359`	`ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NO INHERIT;`
`1360`	`1360`	`ERROR: constraint "fktable_fk_fkey" of relation "fktable" is not a not-null constraint`
`1361`	`1361`	`ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT VALID;`
`1362`		`-ERROR: FOREIGN KEY constraints cannot be marked NOT VALID`
	`1362`	`+ERROR: constraints cannot be altered to be NOT VALID`
`1363`	`1363`	`LINE 1: ...ER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey NOT VALID;`
`1364`	`1364`	`^`
`1365`	`1365`	`ALTER TABLE fktable ALTER CONSTRAINT fktable_fk_fkey ENFORCED NOT ENFORCED;`