ATTACH PARTITION: Don't match a PK with a UNIQUE constraint

When matching constraints in AttachPartitionEnsureIndexes() we weren't
testing the constraint type, which could make a UNIQUE key lacking a
not-null constraint incorrectly satisfy a primary key requirement.  Fix
this by testing that the constraint types match.  (Other possible
mismatches are verified by comparing index properties.)

Discussion: https://postgr.es/m/202402051447.wimb4xmtiiyb@alvherre.pgsql

src/backend/commands/tablecmds.c

@@ -19550,6 +19550,11 @@ AttachPartitionEnsureIndexes(List **wqueue, Relation rel, Relation attachrel)
 					/* no dice */
 					if (!OidIsValid(cldConstrOid))
 						continue;
+
+					/* Ensure they're both the same type of constraint */
+					if (get_constraint_type(constraintOid) !=
+						get_constraint_type(cldConstrOid))
+						continue;
 				}
 
 				/* bingo. */

src/backend/utils/cache/lsyscache.c

@@ -1133,6 +1133,28 @@ get_constraint_index(Oid conoid)
 		return InvalidOid;
 }
 
+/*
+ * get_constraint_type
+ *		Return the pg_constraint.contype value for the given constraint.
+ *
+ * No frills.
+ */
+char
+get_constraint_type(Oid conoid)
+{
+	HeapTuple	tp;
+	char		contype;
+
+	tp = SearchSysCache1(CONSTROID, ObjectIdGetDatum(conoid));
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for constraint %u", conoid);
+
+	contype = ((Form_pg_constraint) GETSTRUCT(tp))->contype;
+	ReleaseSysCache(tp);
+
+	return contype;
+}
+
 /*				---------- LANGUAGE CACHE ----------					 */
 
 char *

src/include/utils/lsyscache.h

@@ -100,6 +100,8 @@ extern char *get_collation_name(Oid colloid);
 extern bool get_collation_isdeterministic(Oid colloid);
 extern char *get_constraint_name(Oid conoid);
 extern Oid	get_constraint_index(Oid conoid);
+extern char get_constraint_type(Oid conoid);
+
 extern char *get_language_name(Oid langoid, bool missing_ok);
 extern Oid	get_opclass_family(Oid opclass);
 extern Oid	get_opclass_input_type(Oid opclass);

src/test/regress/expected/constraints.out

@@ -1006,6 +1006,22 @@ Inherits: cnn_grandchild,
 ALTER TABLE cnn_parent DROP CONSTRAINT cnn_parent_pkey;
 ERROR:  constraint "cnn_parent_pkey" of relation "cnn_parent" does not exist
 -- keeps these tables around, for pg_upgrade testing
+-- A primary key shouldn't attach to a unique constraint
+create table cnn2_parted (a int primary key) partition by list (a);
+create table cnn2_part1 (a int unique);
+alter table cnn2_parted attach partition cnn2_part1 for values in (1);
+\d+ cnn2_part1
+                                Table "public.cnn2_part1"
+ Column |  Type   | Collation | Nullable | Default | Storage | Stats target | Description 
+--------+---------+-----------+----------+---------+---------+--------------+-------------
+ a      | integer |           | not null |         | plain   |              | 
+Partition of: cnn2_parted FOR VALUES IN (1)
+Partition constraint: ((a IS NOT NULL) AND (a = 1))
+Indexes:
+    "cnn2_part1_pkey" PRIMARY KEY, btree (a)
+    "cnn2_part1_a_key" UNIQUE CONSTRAINT, btree (a)
+
+drop table cnn2_parted;
 -- ensure columns in partitions are marked not-null
 create table cnn2_parted(a int primary key) partition by list (a);
 create table cnn2_part1(a int);

src/test/regress/sql/constraints.sql

@@ -657,6 +657,13 @@ ALTER TABLE cnn_parent ADD PRIMARY KEY USING INDEX b_uq;
 ALTER TABLE cnn_parent DROP CONSTRAINT cnn_parent_pkey;
 -- keeps these tables around, for pg_upgrade testing
 
+-- A primary key shouldn't attach to a unique constraint
+create table cnn2_parted (a int primary key) partition by list (a);
+create table cnn2_part1 (a int unique);
+alter table cnn2_parted attach partition cnn2_part1 for values in (1);
+\d+ cnn2_part1
+drop table cnn2_parted;
+
 -- ensure columns in partitions are marked not-null
 create table cnn2_parted(a int primary key) partition by list (a);
 create table cnn2_part1(a int);