Add tests for allowing SET NULL/DEFAULT for subseet of columns

PG 15 added support for that (d6f96ed94e73052f99a2e545ed17a8b2fdc1fb8a).

We also add support, but we already do not support ON DELETE SET NULL/DEFAULT
for distribution column. So, in essence, we add support for reference tables
and Citus local tables.

src/test/regress/expected/pg15.out

@@ -552,7 +552,66 @@ SELECT count(*)=100 FROM copy_test2;
  t
 (1 row)
 
+-- allow foreign key columns to have SET NULL/DEFAULT on column basis
+-- currently only reference tables can support that
+CREATE TABLE PKTABLE (tid int, id int, PRIMARY KEY (tid, id));
+CREATE TABLE FKTABLE (
+  tid int, id int,
+  fk_id_del_set_null int,
+  fk_id_del_set_default int DEFAULT 0,
+  FOREIGN KEY (tid, fk_id_del_set_null) REFERENCES PKTABLE ON DELETE SET NULL (fk_id_del_set_null),
+  FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES PKTABLE ON DELETE SET DEFAULT (fk_id_del_set_default)
+);
+SELECT create_reference_table('PKTABLE');
+ create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- ok, Citus could relax this constraint in the future
+SELECT create_distributed_table('FKTABLE', 'tid');
+ERROR:  cannot create foreign key constraint
+DETAIL:  SET NULL or SET DEFAULT is not supported in ON DELETE operation when distribution key is included in the foreign key constraint
+-- with reference tables it should all work fine
+SELECT create_reference_table('FKTABLE');
+ create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- show that the definition is expected
+SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conrelid = 'fktable'::regclass::oid ORDER BY oid;
+                                                pg_get_constraintdef
+---------------------------------------------------------------------
+ FOREIGN KEY (tid, fk_id_del_set_null) REFERENCES pktable(tid, id) ON DELETE SET NULL (fk_id_del_set_null)
+ FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES pktable(tid, id) ON DELETE SET DEFAULT (fk_id_del_set_default)
+(2 rows)
+
+\c - - - :worker_1_port
+SET search_path TO pg15;
+-- show that the definition is expected on the worker as well
+SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conrelid = 'fktable'::regclass::oid ORDER BY oid;
+                                                pg_get_constraintdef
+---------------------------------------------------------------------
+ FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES pktable(tid, id) ON DELETE SET DEFAULT (fk_id_del_set_default)
+ FOREIGN KEY (tid, fk_id_del_set_null) REFERENCES pktable(tid, id) ON DELETE SET NULL (fk_id_del_set_null)
+(2 rows)
+
+-- also, make sure that it works as expected
+INSERT INTO PKTABLE VALUES (1, 0), (1, 1), (1, 2);
+INSERT INTO FKTABLE VALUES
+  (1, 1, 1, NULL),
+  (1, 2, NULL, 2);
+DELETE FROM PKTABLE WHERE id = 1 OR id = 2;
+SELECT * FROM FKTABLE ORDER BY id;
+ tid | id | fk_id_del_set_null | fk_id_del_set_default
+---------------------------------------------------------------------
+   1 |  1 |                    |
+   1 |  2 |                    |                     0
+(2 rows)
+
 -- Clean up
+\c - - - :master_port
 \set VERBOSITY terse
 DROP SCHEMA pg15 CASCADE;
-NOTICE:  drop cascades to 13 other objects
+NOTICE:  drop cascades to 15 other objects

src/test/regress/sql/pg15.sql

@@ -298,6 +298,47 @@ ALTER TABLE copy_test2 RENAME COLUMN data_ TO data;
 COPY copy_test2 FROM :'temp_dir''copy_test.txt' WITH ( HEADER match, FORMAT text);
 SELECT count(*)=100 FROM copy_test2;
 
+
+-- allow foreign key columns to have SET NULL/DEFAULT on column basis
+-- currently only reference tables can support that
+CREATE TABLE PKTABLE (tid int, id int, PRIMARY KEY (tid, id));
+CREATE TABLE FKTABLE (
+  tid int, id int,
+  fk_id_del_set_null int,
+  fk_id_del_set_default int DEFAULT 0,
+  FOREIGN KEY (tid, fk_id_del_set_null) REFERENCES PKTABLE ON DELETE SET NULL (fk_id_del_set_null),
+  FOREIGN KEY (tid, fk_id_del_set_default) REFERENCES PKTABLE ON DELETE SET DEFAULT (fk_id_del_set_default)
+);
+
+SELECT create_reference_table('PKTABLE');
+
+-- ok, Citus could relax this constraint in the future
+SELECT create_distributed_table('FKTABLE', 'tid');
+
+-- with reference tables it should all work fine
+SELECT create_reference_table('FKTABLE');
+
+-- show that the definition is expected
+SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conrelid = 'fktable'::regclass::oid ORDER BY oid;
+
+\c - - - :worker_1_port
+
+SET search_path TO pg15;
+
+-- show that the definition is expected on the worker as well
+SELECT pg_get_constraintdef(oid) FROM pg_constraint WHERE conrelid = 'fktable'::regclass::oid ORDER BY oid;
+
+-- also, make sure that it works as expected
+INSERT INTO PKTABLE VALUES (1, 0), (1, 1), (1, 2);
+INSERT INTO FKTABLE VALUES
+  (1, 1, 1, NULL),
+  (1, 2, NULL, 2);
+DELETE FROM PKTABLE WHERE id = 1 OR id = 2;
+SELECT * FROM FKTABLE ORDER BY id;
+
+
 -- Clean up
+\c - - - :master_port
+
 \set VERBOSITY terse
 DROP SCHEMA pg15 CASCADE;