PG17 Compatibility: Support MERGE features in Citus with clean exceptions (#7781)

- Adapted `pgmerge.sql` tests from PostgreSQL community's `merge.sql` to
Citus by converting tables into Citus local tables.
- Identified two new PostgreSQL 17 MERGE features (`RETURNING` support
and MERGE on updatable views) not yet supported by Citus.
- Implemented changes to detect unsupported features and raise clean
exceptions, ensuring pgmerge tests pass without diffs.
- Addressed breaking changes caused by `MERGE ... WHEN NOT MATCHED BY
SOURCE` restructuring, reducing diffs in pgmerge tests.
- Segregated unsupported test cases into `merge_unsupported.sql` to
maintain clarity and avoid large diffs in test files.
- Prepared the Citus MERGE planner to handle new PostgreSQL changes,
reducing remaining test discrepancies.

All merge tests now pass cleanly, with unsupported cases clearly
isolated.

Relevant PG commits:
c649fa24a
https://github.com/postgres/postgres/commit/c649fa24a
0294df2f1
https://github.com/postgres/postgres/commit/0294df2f1
---------

Co-authored-by: naisila <nicypp@gmail.com>

src/backend/distributed/commands/multi_copy.c

@@ -346,6 +346,7 @@ static LocalCopyStatus GetLocalCopyStatus(void);
 static bool ShardIntervalListHasLocalPlacements(List *shardIntervalList);
 static void LogLocalCopyToRelationExecution(uint64 shardId);
 static void LogLocalCopyToFileExecution(uint64 shardId);
+static void ErrorIfMergeInCopy(CopyStmt *copyStatement);
 
 
 /* exports for SQL callable functions */
@@ -2823,6 +2824,32 @@ CopyStatementHasFormat(CopyStmt *copyStatement, char *formatName)
 }
 
 
+/*
+ * ErrorIfMergeInCopy Raises an exception if the MERGE is called in the COPY
+ * where Citus tables are involved, as we don't support this yet
+ * Relevant PG17 commit: c649fa24a
+ */
+static void
+ErrorIfMergeInCopy(CopyStmt *copyStatement)
+{
+#if PG_VERSION_NUM < 170000
+	return;
+#else
+	if (!copyStatement->relation && (IsA(copyStatement->query, MergeStmt)))
+	{
+		/*
+		 * This path is currently not reachable because Merge in COPY can
+		 * only work with a RETURNING clause, and a RETURNING check
+		 * will error out sooner for Citus
+		 */
+		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						errmsg("MERGE with Citus tables "
+							   "is not yet supported in COPY")));
+	}
+#endif
+}
+
+
 /*
  * ProcessCopyStmt handles Citus specific concerns for COPY like supporting
  * COPYing from distributed tables and preventing unsupported actions. The
@@ -2860,6 +2887,8 @@ ProcessCopyStmt(CopyStmt *copyStatement, QueryCompletion *completionTag, const
 	 */
 	if (copyStatement->relation != NULL)
 	{
+		ErrorIfMergeInCopy(copyStatement);
+
 		bool isFrom = copyStatement->is_from;
 
 		/* consider using RangeVarGetRelidExtended to check perms before locking */

src/backend/distributed/planner/merge_planner.c

@@ -97,6 +97,8 @@ static DistributedPlan * CreateNonPushableMergePlan(Oid targetRelationId, uint64
 													plannerRestrictionContext,
 													ParamListInfo boundParams);
 static char * MergeCommandResultIdPrefix(uint64 planId);
+static void ErrorIfMergeHasReturningList(Query *query);
+static Node * GetMergeJoinCondition(Query *mergeQuery);
 
 #endif
 
@@ -156,8 +158,51 @@ CreateMergePlan(uint64 planId, Query *originalQuery, Query *query,
 }
 
 
+/*
+ * GetMergeJoinTree constructs and returns the jointree for a MERGE query.
+ */
+FromExpr *
+GetMergeJoinTree(Query *mergeQuery)
+{
+	FromExpr *mergeJointree = NULL;
+#if PG_VERSION_NUM >= PG_VERSION_17
+
+	/*
+	 * In Postgres 17, the query tree has a specific field for the merge condition.
+	 * For deriving the WhereClauseList from the merge condition, we construct a dummy
+	 * jointree with an empty fromlist. This works because the fromlist of a merge query
+	 * join tree consists of range table references only, and range table references are
+	 * disregarded by the WhereClauseList() walker.
+	 * Relevant PG17 commit: 0294df2f1
+	 */
+	mergeJointree = makeFromExpr(NIL, mergeQuery->mergeJoinCondition);
+#else
+	mergeJointree = mergeQuery->jointree;
+#endif
+
+	return mergeJointree;
+}
+
+
 #if PG_VERSION_NUM >= PG_VERSION_15
 
+
+/*
+ * GetMergeJoinCondition returns the quals of the ON condition
+ */
+static Node *
+GetMergeJoinCondition(Query *mergeQuery)
+{
+	Node *joinCondition = NULL;
+#if PG_VERSION_NUM >= PG_VERSION_17
+	joinCondition = (Node *) mergeQuery->mergeJoinCondition;
+#else
+	joinCondition = (Node *) mergeQuery->jointree->quals;
+#endif
+	return joinCondition;
+}
+
+
 /*
  * CreateRouterMergePlan attempts to create a pushable plan for the given MERGE
  * SQL statement. If the planning fails, the ->planningError is set to a description
@@ -562,7 +607,7 @@ MergeQualAndTargetListFunctionsSupported(Oid resultRelationId, Query *query,
 										 List *targetList, CmdType commandType)
 {
 	uint32 targetRangeTableIndex = query->resultRelation;
-	FromExpr *joinTree = query->jointree;
+	FromExpr *joinTree = GetMergeJoinTree(query);
 	Var *distributionColumn = NULL;
 	if (IsCitusTable(resultRelationId) && HasDistributionKey(resultRelationId))
 	{
@@ -722,8 +767,9 @@ ErrorIfRepartitionMergeNotSupported(Oid targetRelationId, Query *mergeQuery,
 	/*
 	 * Sub-queries and CTEs are not allowed in actions and ON clause
 	 */
-	if (FindNodeMatchingCheckFunction((Node *) mergeQuery->jointree->quals,
+	Node *joinCondition = GetMergeJoinCondition(mergeQuery);
-									  IsNodeSubquery))
+
+	if (FindNodeMatchingCheckFunction(joinCondition, IsNodeSubquery))
 	{
 		ereport(ERROR,
 				(errmsg("Sub-queries and CTEs are not allowed in ON clause for MERGE "
@@ -949,9 +995,26 @@ ConvertSourceRTEIntoSubquery(Query *mergeQuery, RangeTblEntry *sourceRte,
 }
 
 
+/*
+ * ErrorIfMergeHasReturningList raises an exception if the MERGE has
+ * a RETURNING clause, as we don't support this yet for Citus tables
+ * Relevant PG17 commit: c649fa24a
+ */
+static void
+ErrorIfMergeHasReturningList(Query *query)
+{
+	if (query->returningList)
+	{
+		ereport(ERROR, (errmsg("MERGE with RETURNING is not yet supported "
+							   "for Citus tables")));
+	}
+}
+
+
 /*
  * ErrorIfMergeNotSupported Checks for conditions that are not supported in either
  * the routable or repartition strategies. It checks for
+ * - MERGE with a RETURNING clause
  * - Supported table types and their combinations
  * - Check the target lists and quals of both the query and merge actions
  * - Supported CTEs
@@ -959,6 +1022,7 @@ ConvertSourceRTEIntoSubquery(Query *mergeQuery, RangeTblEntry *sourceRte,
 static void
 ErrorIfMergeNotSupported(Query *query, Oid targetRelationId, List *rangeTableList)
 {
+	ErrorIfMergeHasReturningList(query);
 	ErrorIfMergeHasUnsupportedTables(targetRelationId, rangeTableList);
 	ErrorIfMergeQueryQualAndTargetListNotSupported(targetRelationId, query);
 	ErrorIfUnsupportedCTEs(query);
@@ -1207,12 +1271,15 @@ ErrorIfMergeQueryQualAndTargetListNotSupported(Oid targetRelationId, Query *orig
 							   "supported in MERGE sql with distributed tables")));
 	}
 
+	Node *joinCondition = GetMergeJoinCondition(originalQuery);
+
 	DeferredErrorMessage *deferredError =
-		MergeQualAndTargetListFunctionsSupported(targetRelationId,
+		MergeQualAndTargetListFunctionsSupported(
-												 originalQuery,
+			targetRelationId,
-												 originalQuery->jointree->quals,
+			originalQuery,
-												 originalQuery->targetList,
+			joinCondition,
-												 originalQuery->commandType);
+			originalQuery->targetList,
+			originalQuery->commandType);
 
 	if (deferredError)
 	{
@@ -1286,8 +1353,7 @@ static int
 SourceResultPartitionColumnIndex(Query *mergeQuery, List *sourceTargetList,
 								 CitusTableCacheEntry *targetRelation)
 {
-	/* Get all the Join conditions from the ON clause */
+	List *mergeJoinConditionList = WhereClauseList(GetMergeJoinTree(mergeQuery));
-	List *mergeJoinConditionList = WhereClauseList(mergeQuery->jointree);
 	Var *targetColumn = targetRelation->partitionColumn;
 	Var *sourceRepartitionVar = NULL;
 	bool foundTypeMismatch = false;

src/backend/distributed/planner/multi_router_planner.c

@@ -598,8 +598,7 @@ TargetlistAndFunctionsSupported(Oid resultRelationId, FromExpr *joinTree, Node *
 		}
 
 		if (commandType == CMD_UPDATE && targetEntryPartitionColumn &&
-			TargetEntryChangesValue(targetEntry, partitionColumn,
+			TargetEntryChangesValue(targetEntry, partitionColumn, joinTree))
-									joinTree))
 		{
 			return DeferredError(ERRCODE_FEATURE_NOT_SUPPORTED,
 								 "modifying the partition value of rows is not "

src/include/distributed/merge_planner.h

@@ -32,6 +32,7 @@ extern void NonPushableMergeCommandExplainScan(CustomScanState *node, List *ance
 											   struct ExplainState *es);
 extern Var * FetchAndValidateInsertVarIfExists(Oid targetRelationId, Query *query);
 extern RangeTblEntry * ExtractMergeSourceRangeTableEntry(Query *query, bool joinSourceOk);
+extern FromExpr * GetMergeJoinTree(Query *mergeQuery);
 
 
 #endif /* MERGE_PLANNER_H */

src/test/regress/expected/merge_unsupported.out

@@ -0,0 +1,101 @@
+SHOW server_version \gset
+SELECT CASE
+           WHEN substring(current_setting('server_version'), '\d+')::int >= 17 THEN '17+'
+           WHEN substring(current_setting('server_version'), '\d+')::int IN (15, 16) THEN '15_16'
+           WHEN substring(current_setting('server_version'), '\d+')::int = 14 THEN '14'
+           ELSE 'Unsupported version'
+       END AS version_category;
+ version_category
+---------------------------------------------------------------------
+ 17+
+(1 row)
+
+SELECT substring(:'server_version', '\d+')::int >= 15 AS server_version_ge_15
+\gset
+\if :server_version_ge_15
+\else
+\q
+\endif
+--
+-- MERGE test from PG community (adapted to Citus by converting all tables to Citus local)
+--
+DROP SCHEMA IF EXISTS pgmerge_schema CASCADE;
+NOTICE:  schema "pgmerge_schema" does not exist, skipping
+CREATE SCHEMA pgmerge_schema;
+SET search_path TO pgmerge_schema;
+SET citus.use_citus_managed_tables to true;
+CREATE TABLE target (tid integer, balance integer)
+  WITH (autovacuum_enabled=off);
+CREATE TABLE source (sid integer, delta integer) -- no index
+  WITH (autovacuum_enabled=off);
+\set SHOW_CONTEXT errors
+-- used in a CTE
+WITH foo AS (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE
+) SELECT * FROM foo;
+ERROR:  WITH query "foo" does not have a RETURNING clause
+-- used in COPY
+COPY (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE
+) TO stdout;
+ERROR:  COPY query must have a RETURNING clause
+-- used in a CTE with RETURNING
+WITH foo AS (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE RETURNING target.*
+) SELECT * FROM foo;
+ERROR:  MERGE with RETURNING is not yet supported for Citus tables
+-- used in COPY with RETURNING
+COPY (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE RETURNING target.*
+) TO stdout;
+ERROR:  MERGE with RETURNING is not yet supported for Citus tables
+-- unsupported relation types
+-- view
+CREATE VIEW tv AS SELECT count(tid) AS tid FROM target;
+MERGE INTO tv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+ERROR:  cannot insert into view "tv"
+DETAIL:  Views that return aggregate functions are not automatically updatable.
+HINT:  To enable inserting into the view using MERGE, provide an INSTEAD OF INSERT trigger.
+DROP VIEW tv;
+CREATE TABLE sq_target (tid integer NOT NULL, balance integer)
+  WITH (autovacuum_enabled=off);
+CREATE TABLE sq_source (delta integer, sid integer, balance integer DEFAULT 0)
+  WITH (autovacuum_enabled=off);
+SELECT citus_add_local_table_to_metadata('sq_target');
+ citus_add_local_table_to_metadata
+---------------------------------------------------------------------
+
+(1 row)
+
+SELECT citus_add_local_table_to_metadata('sq_source');
+ citus_add_local_table_to_metadata
+---------------------------------------------------------------------
+
+(1 row)
+
+INSERT INTO sq_target(tid, balance) VALUES (1,100), (2,200), (3,300);
+INSERT INTO sq_source(sid, delta) VALUES (1,10), (2,20), (4,40);
+CREATE VIEW v AS SELECT * FROM sq_source WHERE sid < 2;
+-- RETURNING
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+        INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+        DELETE
+RETURNING *;
+ERROR:  MERGE with RETURNING is not yet supported for Citus tables
+ROLLBACK;

src/test/regress/expected/merge_unsupported_0.out

@@ -0,0 +1,100 @@
+SHOW server_version \gset
+SELECT CASE
+           WHEN substring(current_setting('server_version'), '\d+')::int >= 17 THEN '17+'
+           WHEN substring(current_setting('server_version'), '\d+')::int IN (15, 16) THEN '15_16'
+           WHEN substring(current_setting('server_version'), '\d+')::int = 14 THEN '14'
+           ELSE 'Unsupported version'
+       END AS version_category;
+ version_category
+---------------------------------------------------------------------
+ 15_16
+(1 row)
+
+SELECT substring(:'server_version', '\d+')::int >= 15 AS server_version_ge_15
+\gset
+\if :server_version_ge_15
+\else
+\q
+\endif
+--
+-- MERGE test from PG community (adapted to Citus by converting all tables to Citus local)
+--
+DROP SCHEMA IF EXISTS pgmerge_schema CASCADE;
+NOTICE:  schema "pgmerge_schema" does not exist, skipping
+CREATE SCHEMA pgmerge_schema;
+SET search_path TO pgmerge_schema;
+SET citus.use_citus_managed_tables to true;
+CREATE TABLE target (tid integer, balance integer)
+  WITH (autovacuum_enabled=off);
+CREATE TABLE source (sid integer, delta integer) -- no index
+  WITH (autovacuum_enabled=off);
+\set SHOW_CONTEXT errors
+-- used in a CTE
+WITH foo AS (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE
+) SELECT * FROM foo;
+ERROR:  MERGE not supported in WITH query
+-- used in COPY
+COPY (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE
+) TO stdout;
+ERROR:  MERGE not supported in COPY
+-- used in a CTE with RETURNING
+WITH foo AS (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE RETURNING target.*
+) SELECT * FROM foo;
+ERROR:  syntax error at or near "RETURNING"
+-- used in COPY with RETURNING
+COPY (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE RETURNING target.*
+) TO stdout;
+ERROR:  syntax error at or near "RETURNING"
+-- unsupported relation types
+-- view
+CREATE VIEW tv AS SELECT count(tid) AS tid FROM target;
+MERGE INTO tv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+ERROR:  cannot execute MERGE on relation "tv"
+DETAIL:  This operation is not supported for views.
+DROP VIEW tv;
+CREATE TABLE sq_target (tid integer NOT NULL, balance integer)
+  WITH (autovacuum_enabled=off);
+CREATE TABLE sq_source (delta integer, sid integer, balance integer DEFAULT 0)
+  WITH (autovacuum_enabled=off);
+SELECT citus_add_local_table_to_metadata('sq_target');
+ citus_add_local_table_to_metadata
+---------------------------------------------------------------------
+
+(1 row)
+
+SELECT citus_add_local_table_to_metadata('sq_source');
+ citus_add_local_table_to_metadata
+---------------------------------------------------------------------
+
+(1 row)
+
+INSERT INTO sq_target(tid, balance) VALUES (1,100), (2,200), (3,300);
+INSERT INTO sq_source(sid, delta) VALUES (1,10), (2,20), (4,40);
+CREATE VIEW v AS SELECT * FROM sq_source WHERE sid < 2;
+-- RETURNING
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+        INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+        DELETE
+RETURNING *;
+ERROR:  syntax error at or near "RETURNING"
+ROLLBACK;

src/test/regress/expected/merge_unsupported_1.out

@@ -0,0 +1,17 @@
+SHOW server_version \gset
+SELECT CASE
+           WHEN substring(current_setting('server_version'), '\d+')::int >= 17 THEN '17+'
+           WHEN substring(current_setting('server_version'), '\d+')::int IN (15, 16) THEN '15_16'
+           WHEN substring(current_setting('server_version'), '\d+')::int = 14 THEN '14'
+           ELSE 'Unsupported version'
+       END AS version_category;
+ version_category
+---------------------------------------------------------------------
+ 14
+(1 row)
+
+SELECT substring(:'server_version', '\d+')::int >= 15 AS server_version_ge_15
+\gset
+\if :server_version_ge_15
+\else
+\q

src/test/regress/expected/pg15.out

@@ -437,16 +437,6 @@ MERGE INTO tbl1 USING targq ON (true)
 WHEN MATCHED THEN DELETE;
 ERROR:  The required join operation is missing between the target's distribution column and any expression originating from the source. The issue may arise from a non-equi-join.
 DETAIL:  Without a equi-join condition on the target's distribution column, the source rows cannot be efficiently redistributed, and the NOT-MATCHED condition cannot be evaluated unambiguously. This can result in incorrect or unexpected results when attempting to merge tables in a distributed setting
-WITH foo AS (
-  MERGE INTO tbl1 USING tbl2 ON (true)
-  WHEN MATCHED THEN DELETE
-) SELECT * FROM foo;
-ERROR:  MERGE not supported in WITH query
-COPY (
-  MERGE INTO tbl1 USING tbl2 ON (true)
-  WHEN MATCHED THEN DELETE
-) TO stdout;
-ERROR:  MERGE not supported in COPY
 MERGE INTO tbl1 t
 USING tbl2
 ON (true)

src/test/regress/expected/pgmerge.out

@@ -162,29 +162,7 @@ ON tid = tid
 WHEN MATCHED THEN DO NOTHING;
 ERROR:  name "target" specified more than once
 DETAIL:  The name is used both as MERGE target table and data source.
--- used in a CTE
-WITH foo AS (
-  MERGE INTO target USING source ON (true)
-  WHEN MATCHED THEN DELETE
-) SELECT * FROM foo;
-ERROR:  MERGE not supported in WITH query
--- used in COPY
-COPY (
-  MERGE INTO target USING source ON (true)
-  WHEN MATCHED THEN DELETE
-) TO stdout;
-ERROR:  MERGE not supported in COPY
 -- unsupported relation types
--- view
-CREATE VIEW tv AS SELECT * FROM target;
-MERGE INTO tv t
-USING source s
-ON t.tid = s.sid
-WHEN NOT MATCHED THEN
-	INSERT DEFAULT VALUES;
-ERROR:  cannot execute MERGE on relation "tv"
-DETAIL:  This operation is not supported for views.
-DROP VIEW tv;
 -- materialized view
 CREATE MATERIALIZED VIEW mv AS SELECT * FROM target;
 MERGE INTO mv t
@@ -1376,21 +1354,6 @@ WHEN NOT MATCHED THEN
 WHEN MATCHED AND tid < 2 THEN
 	DELETE;
 ROLLBACK;
--- RETURNING
-BEGIN;
-INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
-MERGE INTO sq_target t
-USING v
-ON tid = sid
-WHEN MATCHED AND tid > 2 THEN
-    UPDATE SET balance = t.balance + delta
-WHEN NOT MATCHED THEN
-	INSERT (balance, tid) VALUES (balance + delta, sid)
-WHEN MATCHED AND tid < 2 THEN
-	DELETE
-RETURNING *;
-ERROR:  syntax error at or near "RETURNING"
-ROLLBACK;
 -- EXPLAIN
 CREATE TABLE ex_mtarget (a int, b int)
   WITH (autovacuum_enabled=off);

src/test/regress/multi_schedule

@@ -120,7 +120,7 @@ test: merge pgmerge
 test: merge_repartition2
 test: merge_repartition1 merge_schema_sharding
 test: merge_partition_tables
-test: merge_vcore
+test: merge_vcore merge_unsupported
 
 # ---------
 # test that no tests leaked intermediate results. This should always be last

src/test/regress/sql/merge_unsupported.sql

@@ -0,0 +1,89 @@
+
+
+SHOW server_version \gset
+SELECT CASE
+           WHEN substring(current_setting('server_version'), '\d+')::int >= 17 THEN '17+'
+           WHEN substring(current_setting('server_version'), '\d+')::int IN (15, 16) THEN '15_16'
+           WHEN substring(current_setting('server_version'), '\d+')::int = 14 THEN '14'
+           ELSE 'Unsupported version'
+       END AS version_category;
+SELECT substring(:'server_version', '\d+')::int >= 15 AS server_version_ge_15
+\gset
+\if :server_version_ge_15
+\else
+\q
+\endif
+
+--
+-- MERGE test from PG community (adapted to Citus by converting all tables to Citus local)
+--
+DROP SCHEMA IF EXISTS pgmerge_schema CASCADE;
+CREATE SCHEMA pgmerge_schema;
+SET search_path TO pgmerge_schema;
+
+SET citus.use_citus_managed_tables to true;
+
+CREATE TABLE target (tid integer, balance integer)
+  WITH (autovacuum_enabled=off);
+CREATE TABLE source (sid integer, delta integer) -- no index
+  WITH (autovacuum_enabled=off);
+
+\set SHOW_CONTEXT errors
+-- used in a CTE
+WITH foo AS (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE
+) SELECT * FROM foo;
+-- used in COPY
+COPY (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE
+) TO stdout;
+-- used in a CTE with RETURNING
+WITH foo AS (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE RETURNING target.*
+) SELECT * FROM foo;
+-- used in COPY with RETURNING
+COPY (
+  MERGE INTO target USING source ON (true)
+  WHEN MATCHED THEN DELETE RETURNING target.*
+) TO stdout;
+
+-- unsupported relation types
+-- view
+CREATE VIEW tv AS SELECT count(tid) AS tid FROM target;
+MERGE INTO tv t
+USING source s
+ON t.tid = s.sid
+WHEN NOT MATCHED THEN
+	INSERT DEFAULT VALUES;
+DROP VIEW tv;
+
+CREATE TABLE sq_target (tid integer NOT NULL, balance integer)
+  WITH (autovacuum_enabled=off);
+CREATE TABLE sq_source (delta integer, sid integer, balance integer DEFAULT 0)
+  WITH (autovacuum_enabled=off);
+
+SELECT citus_add_local_table_to_metadata('sq_target');
+SELECT citus_add_local_table_to_metadata('sq_source');
+
+INSERT INTO sq_target(tid, balance) VALUES (1,100), (2,200), (3,300);
+INSERT INTO sq_source(sid, delta) VALUES (1,10), (2,20), (4,40);
+
+CREATE VIEW v AS SELECT * FROM sq_source WHERE sid < 2;
+
+-- RETURNING
+BEGIN;
+INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
+MERGE INTO sq_target t
+USING v
+ON tid = sid
+WHEN MATCHED AND tid > 2 THEN
+    UPDATE SET balance = t.balance + delta
+WHEN NOT MATCHED THEN
+        INSERT (balance, tid) VALUES (balance + delta, sid)
+WHEN MATCHED AND tid < 2 THEN
+        DELETE
+RETURNING *;
+ROLLBACK;

src/test/regress/sql/pg15.sql

@@ -287,16 +287,6 @@ WITH targq AS (
 MERGE INTO tbl1 USING targq ON (true)
 WHEN MATCHED THEN DELETE;
 
-WITH foo AS (
-  MERGE INTO tbl1 USING tbl2 ON (true)
-  WHEN MATCHED THEN DELETE
-) SELECT * FROM foo;
-
-COPY (
-  MERGE INTO tbl1 USING tbl2 ON (true)
-  WHEN MATCHED THEN DELETE
-) TO stdout;
-
 MERGE INTO tbl1 t
 USING tbl2
 ON (true)

src/test/regress/sql/pgmerge.sql

@@ -116,27 +116,8 @@ MERGE INTO target
 USING target
 ON tid = tid
 WHEN MATCHED THEN DO NOTHING;
--- used in a CTE
-WITH foo AS (
-  MERGE INTO target USING source ON (true)
-  WHEN MATCHED THEN DELETE
-) SELECT * FROM foo;
--- used in COPY
-COPY (
-  MERGE INTO target USING source ON (true)
-  WHEN MATCHED THEN DELETE
-) TO stdout;
 
 -- unsupported relation types
--- view
-CREATE VIEW tv AS SELECT * FROM target;
-MERGE INTO tv t
-USING source s
-ON t.tid = s.sid
-WHEN NOT MATCHED THEN
-	INSERT DEFAULT VALUES;
-DROP VIEW tv;
-
 -- materialized view
 CREATE MATERIALIZED VIEW mv AS SELECT * FROM target;
 MERGE INTO mv t
@@ -905,21 +886,6 @@ WHEN MATCHED AND tid < 2 THEN
 	DELETE;
 ROLLBACK;
 
--- RETURNING
-BEGIN;
-INSERT INTO sq_source (sid, balance, delta) VALUES (-1, -1, -10);
-MERGE INTO sq_target t
-USING v
-ON tid = sid
-WHEN MATCHED AND tid > 2 THEN
-    UPDATE SET balance = t.balance + delta
-WHEN NOT MATCHED THEN
-	INSERT (balance, tid) VALUES (balance + delta, sid)
-WHEN MATCHED AND tid < 2 THEN
-	DELETE
-RETURNING *;
-ROLLBACK;
-
 -- EXPLAIN
 CREATE TABLE ex_mtarget (a int, b int)
   WITH (autovacuum_enabled=off);