Detach constraints when partitions are detached

I (Álvaro) forgot to do this in eb7ed3f306, leading to undroppable
constraints after partitions are detached.  Repair.

Reported-by: Amit Langote
Author: Amit Langote
Discussion: https://postgr.es/m/c1c9b688-b886-84f7-4048-1e4ebe9b1d06@lab.ntt.co.jp

src/backend/commands/tablecmds.c

@@ -15095,6 +15095,7 @@ ATExecDetachPartition(Relation rel, RangeVar *name)
 	{
 		Oid			idxid = lfirst_oid(cell);
 		Relation	idx;
+		Oid			constrOid;
 
 		if (!has_superclass(idxid))
 			continue;
@@ -15106,6 +15107,23 @@ ATExecDetachPartition(Relation rel, RangeVar *name)
 		IndexSetParentIndex(idx, InvalidOid);
 		update_relispartition(classRel, idxid, false);
 		index_close(idx, NoLock);
+
+		/*
+		 * Detach any constraints associated with the index too.  Only UNIQUE
+		 * and PRIMARY KEY index constraints can be inherited, so no need
+		 * to check for others.
+		 */
+		if (!idx->rd_index->indisprimary && !idx->rd_index->indisunique)
+			continue;
+
+		constrOid = get_relation_idx_constraint_oid(RelationGetRelid(partRel),
+													idxid);
+		if (!OidIsValid(constrOid))
+			elog(ERROR, "missing pg_constraint entry of index \"%s\" of partition \"%s\"",
+				 RelationGetRelationName(idx),
+				 RelationGetRelationName(partRel));
+
+		ConstraintSetParentConstraint(constrOid, InvalidOid);
 	}
 	table_close(classRel, RowExclusiveLock);
 

src/test/regress/expected/indexing.out

@@ -1414,3 +1414,18 @@ DETAIL:  Key (a)=(4) already exists.
 create unique index on covidxpart (b) include (a); -- should fail
 ERROR:  insufficient columns in UNIQUE constraint definition
 DETAIL:  UNIQUE constraint on table "covidxpart" lacks column "a" which is part of the partition key.
+-- check that detaching a partition also detaches the primary key constraint
+create table parted_pk_detach_test (a int primary key) partition by list (a);
+create table parted_pk_detach_test1 partition of parted_pk_detach_test for values in (1);
+alter table parted_pk_detach_test1 drop constraint parted_pk_detach_test1_pkey;	-- should fail
+ERROR:  cannot drop inherited constraint "parted_pk_detach_test1_pkey" of relation "parted_pk_detach_test1"
+alter table parted_pk_detach_test detach partition parted_pk_detach_test1;
+alter table parted_pk_detach_test1 drop constraint parted_pk_detach_test1_pkey;
+drop table parted_pk_detach_test, parted_pk_detach_test1;
+create table parted_uniq_detach_test (a int unique) partition by list (a);
+create table parted_uniq_detach_test1 partition of parted_uniq_detach_test for values in (1);
+alter table parted_uniq_detach_test1 drop constraint parted_uniq_detach_test1_a_key;	-- should fail
+ERROR:  cannot drop inherited constraint "parted_uniq_detach_test1_a_key" of relation "parted_uniq_detach_test1"
+alter table parted_uniq_detach_test detach partition parted_uniq_detach_test1;
+alter table parted_uniq_detach_test1 drop constraint parted_uniq_detach_test1_a_key;
+drop table parted_uniq_detach_test, parted_uniq_detach_test1;

src/test/regress/sql/indexing.sql

@@ -757,3 +757,17 @@ alter table covidxpart attach partition covidxpart4 for values in (4);
 insert into covidxpart values (4, 1);
 insert into covidxpart values (4, 1);
 create unique index on covidxpart (b) include (a); -- should fail
+
+-- check that detaching a partition also detaches the primary key constraint
+create table parted_pk_detach_test (a int primary key) partition by list (a);
+create table parted_pk_detach_test1 partition of parted_pk_detach_test for values in (1);
+alter table parted_pk_detach_test1 drop constraint parted_pk_detach_test1_pkey;	-- should fail
+alter table parted_pk_detach_test detach partition parted_pk_detach_test1;
+alter table parted_pk_detach_test1 drop constraint parted_pk_detach_test1_pkey;
+drop table parted_pk_detach_test, parted_pk_detach_test1;
+create table parted_uniq_detach_test (a int unique) partition by list (a);
+create table parted_uniq_detach_test1 partition of parted_uniq_detach_test for values in (1);
+alter table parted_uniq_detach_test1 drop constraint parted_uniq_detach_test1_a_key;	-- should fail
+alter table parted_uniq_detach_test detach partition parted_uniq_detach_test1;
+alter table parted_uniq_detach_test1 drop constraint parted_uniq_detach_test1_a_key;
+drop table parted_uniq_detach_test, parted_uniq_detach_test1;