Improve parse representation for MERGE

Separation of parser data structures from executor, as
requested by Tom Lane. Further improvements possible.

While there, implement error for multiple VALUES clauses via parser
to allow line number of error, as requested by Andres Freund.

Author: Pavan Deolasee

Discussion: https://www.postgresql.org/message-id/CABOikdPpqjectFchg0FyTOpsGXyPoqwgC==OLKWuxgBOsrDDZw@mail.gmail.com

src/backend/nodes/copyfuncs.c

@@ -2136,6 +2136,20 @@ _copyOnConflictExpr(const OnConflictExpr *from)
 	return newnode;
 }
 
+static MergeAction *
+_copyMergeAction(const MergeAction *from)
+{
+	MergeAction *newnode = makeNode(MergeAction);
+
+	COPY_SCALAR_FIELD(matched);
+	COPY_SCALAR_FIELD(commandType);
+	COPY_SCALAR_FIELD(override);
+	COPY_NODE_FIELD(qual);
+	COPY_NODE_FIELD(targetList);
+
+	return newnode;
+}
+
 /* ****************************************************************
  *						relation.h copy functions
  *
@@ -3054,24 +3068,24 @@ _copyMergeStmt(const MergeStmt *from)
 	COPY_NODE_FIELD(relation);
 	COPY_NODE_FIELD(source_relation);
 	COPY_NODE_FIELD(join_condition);
-	COPY_NODE_FIELD(mergeActionList);
+	COPY_NODE_FIELD(mergeWhenClauses);
 	COPY_NODE_FIELD(withClause);
 
 	return newnode;
 }
 
-static MergeAction *
-_copyMergeAction(const MergeAction *from)
+static MergeWhenClause *
+_copyMergeWhenClause(const MergeWhenClause *from)
 {
-	MergeAction *newnode = makeNode(MergeAction);
+	MergeWhenClause *newnode = makeNode(MergeWhenClause);
 
 	COPY_SCALAR_FIELD(matched);
 	COPY_SCALAR_FIELD(commandType);
 	COPY_NODE_FIELD(condition);
-	COPY_NODE_FIELD(qual);
-	COPY_NODE_FIELD(stmt);
 	COPY_NODE_FIELD(targetList);
-
+	COPY_NODE_FIELD(cols);
+	COPY_NODE_FIELD(values);
+	COPY_SCALAR_FIELD(override);
 	return newnode;
 }
 
@@ -5059,6 +5073,9 @@ copyObjectImpl(const void *from)
 		case T_OnConflictExpr:
 			retval = _copyOnConflictExpr(from);
 			break;
+		case T_MergeAction:
+			retval = _copyMergeAction(from);
+			break;
 
 			/*
 			 * RELATION NODES
@@ -5140,8 +5157,8 @@ copyObjectImpl(const void *from)
 		case T_MergeStmt:
 			retval = _copyMergeStmt(from);
 			break;
-		case T_MergeAction:
-			retval = _copyMergeAction(from);
+		case T_MergeWhenClause:
+			retval = _copyMergeWhenClause(from);
 			break;
 		case T_SelectStmt:
 			retval = _copySelectStmt(from);

src/backend/nodes/equalfuncs.c

@@ -812,6 +812,18 @@ _equalOnConflictExpr(const OnConflictExpr *a, const OnConflictExpr *b)
 	return true;
 }
 
+
+static bool
+_equalMergeAction(const MergeAction *a, const MergeAction *b)
+{
+	COMPARE_SCALAR_FIELD(matched);
+	COMPARE_SCALAR_FIELD(commandType);
+	COMPARE_SCALAR_FIELD(override);
+	COMPARE_NODE_FIELD(qual);
+	COMPARE_NODE_FIELD(targetList);
+
+	return true;
+}
 /*
  * Stuff from relation.h
  */
@@ -1050,21 +1062,22 @@ _equalMergeStmt(const MergeStmt *a, const MergeStmt *b)
 	COMPARE_NODE_FIELD(relation);
 	COMPARE_NODE_FIELD(source_relation);
 	COMPARE_NODE_FIELD(join_condition);
-	COMPARE_NODE_FIELD(mergeActionList);
+	COMPARE_NODE_FIELD(mergeWhenClauses);
 	COMPARE_NODE_FIELD(withClause);
 
 	return true;
 }
 
 static bool
-_equalMergeAction(const MergeAction *a, const MergeAction *b)
+_equalMergeWhenClause(const MergeWhenClause *a, const MergeWhenClause *b)
 {
 	COMPARE_SCALAR_FIELD(matched);
 	COMPARE_SCALAR_FIELD(commandType);
 	COMPARE_NODE_FIELD(condition);
-	COMPARE_NODE_FIELD(qual);
-	COMPARE_NODE_FIELD(stmt);
 	COMPARE_NODE_FIELD(targetList);
+	COMPARE_NODE_FIELD(cols);
+	COMPARE_NODE_FIELD(values);
+	COMPARE_SCALAR_FIELD(override);
 
 	return true;
 }
@@ -3192,6 +3205,9 @@ equal(const void *a, const void *b)
 		case T_OnConflictExpr:
 			retval = _equalOnConflictExpr(a, b);
 			break;
+		case T_MergeAction:
+			retval = _equalMergeAction(a, b);
+			break;
 		case T_JoinExpr:
 			retval = _equalJoinExpr(a, b);
 			break;
@@ -3263,8 +3279,8 @@ equal(const void *a, const void *b)
 		case T_MergeStmt:
 			retval = _equalMergeStmt(a, b);
 			break;
-		case T_MergeAction:
-			retval = _equalMergeAction(a, b);
+		case T_MergeWhenClause:
+			retval = _equalMergeWhenClause(a, b);
 			break;
 		case T_SelectStmt:
 			retval = _equalSelectStmt(a, b);

src/backend/nodes/nodeFuncs.c

@@ -3444,19 +3444,23 @@ raw_expression_tree_walker(Node *node,
 					return true;
 				if (walker(stmt->join_condition, context))
 					return true;
-				if (walker(stmt->mergeActionList, context))
+				if (walker(stmt->mergeWhenClauses, context))
 					return true;
 				if (walker(stmt->withClause, context))
 					return true;
 			}
 			break;
-		case T_MergeAction:
+		case T_MergeWhenClause:
 			{
-				MergeAction *action = (MergeAction *) node;
+				MergeWhenClause *mergeWhenClause = (MergeWhenClause *) node;
 
-				if (walker(action->targetList, context))
+				if (walker(mergeWhenClause->condition, context))
 					return true;
-				if (walker(action->qual, context))
+				if (walker(mergeWhenClause->targetList, context))
+					return true;
+				if (walker(mergeWhenClause->cols, context))
+					return true;
+				if (walker(mergeWhenClause->values, context))
 					return true;
 			}
 			break;

src/backend/nodes/outfuncs.c

@@ -396,16 +396,17 @@ _outModifyTable(StringInfo str, const ModifyTable *node)
 }
 
 static void
-_outMergeAction(StringInfo str, const MergeAction *node)
+_outMergeWhenClause(StringInfo str, const MergeWhenClause *node)
 {
-	WRITE_NODE_TYPE("MERGEACTION");
+	WRITE_NODE_TYPE("MERGEWHENCLAUSE");
 
 	WRITE_BOOL_FIELD(matched);
 	WRITE_ENUM_FIELD(commandType, CmdType);
 	WRITE_NODE_FIELD(condition);
-	WRITE_NODE_FIELD(qual);
-	WRITE_NODE_FIELD(stmt);
 	WRITE_NODE_FIELD(targetList);
+	WRITE_NODE_FIELD(cols);
+	WRITE_NODE_FIELD(values);
+	WRITE_ENUM_FIELD(override, OverridingKind);
 }
 
 static void
@@ -1724,6 +1725,17 @@ _outOnConflictExpr(StringInfo str, const OnConflictExpr *node)
 	WRITE_NODE_FIELD(exclRelTlist);
 }
 
+static void
+_outMergeAction(StringInfo str, const MergeAction *node)
+{
+	WRITE_NODE_TYPE("MERGEACTION");
+
+	WRITE_BOOL_FIELD(matched);
+	WRITE_ENUM_FIELD(commandType, CmdType);
+	WRITE_NODE_FIELD(qual);
+	WRITE_NODE_FIELD(targetList);
+}
+
 /*****************************************************************************
  *
  *	Stuff from relation.h.
@@ -3679,8 +3691,8 @@ outNode(StringInfo str, const void *obj)
 			case T_ModifyTable:
 				_outModifyTable(str, obj);
 				break;
-			case T_MergeAction:
-				_outMergeAction(str, obj);
+			case T_MergeWhenClause:
+				_outMergeWhenClause(str, obj);
 				break;
 			case T_Append:
 				_outAppend(str, obj);
@@ -3958,6 +3970,9 @@ outNode(StringInfo str, const void *obj)
 			case T_OnConflictExpr:
 				_outOnConflictExpr(str, obj);
 				break;
+			case T_MergeAction:
+				_outMergeAction(str, obj);
+				break;
 			case T_Path:
 				_outPath(str, obj);
 				break;

src/backend/nodes/readfuncs.c

@@ -1331,6 +1331,22 @@ _readOnConflictExpr(void)
 	READ_DONE();
 }
 
+/*
+ * _readMergeAction
+ */
+static MergeAction *
+_readMergeAction(void)
+{
+	READ_LOCALS(MergeAction);
+
+	READ_BOOL_FIELD(matched);
+	READ_ENUM_FIELD(commandType, CmdType);
+	READ_NODE_FIELD(qual);
+	READ_NODE_FIELD(targetList);
+
+	READ_DONE();
+}
+
 /*
  *	Stuff from parsenodes.h.
  */
@@ -1602,19 +1618,20 @@ _readModifyTable(void)
 }
 
 /*
- * _readMergeAction
+ * _readMergeWhenClause
  */
-static MergeAction *
-_readMergeAction(void)
+static MergeWhenClause *
+_readMergeWhenClause(void)
 {
-	READ_LOCALS(MergeAction);
+	READ_LOCALS(MergeWhenClause);
 
 	READ_BOOL_FIELD(matched);
 	READ_ENUM_FIELD(commandType, CmdType);
 	READ_NODE_FIELD(condition);
-	READ_NODE_FIELD(qual);
-	READ_NODE_FIELD(stmt);
 	READ_NODE_FIELD(targetList);
+	READ_NODE_FIELD(cols);
+	READ_NODE_FIELD(values);
+	READ_ENUM_FIELD(override, OverridingKind);
 
 	READ_DONE();
 }
@@ -2596,6 +2613,8 @@ parseNodeString(void)
 		return_value = _readFromExpr();
 	else if (MATCH("ONCONFLICTEXPR", 14))
 		return_value = _readOnConflictExpr();
+	else if (MATCH("MERGEACTION", 11))
+		return_value = _readMergeAction();
 	else if (MATCH("RTE", 3))
 		return_value = _readRangeTblEntry();
 	else if (MATCH("RANGETBLFUNCTION", 16))
@@ -2618,8 +2637,8 @@ parseNodeString(void)
 		return_value = _readProjectSet();
 	else if (MATCH("MODIFYTABLE", 11))
 		return_value = _readModifyTable();
-	else if (MATCH("MERGEACTION", 11))
-		return_value = _readMergeAction();
+	else if (MATCH("MERGEWHENCLAUSE", 15))
+		return_value = _readMergeWhenClause();
 	else if (MATCH("APPEND", 6))
 		return_value = _readAppend();
 	else if (MATCH("MERGEAPPEND", 11))

src/backend/parser/gram.y

@@ -241,6 +241,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	PartitionSpec		*partspec;
 	PartitionBoundSpec	*partboundspec;
 	RoleSpec			*rolespec;
+	MergeWhenClause		*mergewhen;
 }
 
 %type <node>	stmt schema_stmt
@@ -400,6 +401,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 				TriggerTransitions TriggerReferencing
 				publication_name_list
 				vacuum_relation_list opt_vacuum_relation_list
+				merge_values_clause
 
 %type <list>	group_by_list
 %type <node>	group_by_item empty_grouping_set rollup_clause cube_clause
@@ -460,6 +462,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <istmt>	insert_rest
 %type <infer>	opt_conf_expr
 %type <onconflict> opt_on_conflict
+%type <mergewhen>	merge_insert merge_update merge_delete
 
 %type <vsetstmt> generic_set set_rest set_rest_more generic_reset reset_rest
 				 SetResetClause FunctionSetResetClause
@@ -587,7 +590,6 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 %type <node>	merge_when_clause opt_merge_when_and_condition
 %type <list>	merge_when_list
-%type <node>	merge_update merge_delete merge_insert
 
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
@@ -11116,7 +11118,7 @@ MergeStmt:
 					m->relation = $4;
 					m->source_relation = $6;
 					m->join_condition = $8;
-					m->mergeActionList = $9;
+					m->mergeWhenClauses = $9;
 
 					$$ = (Node *)m;
 				}
@@ -11131,45 +11133,37 @@ merge_when_list:
 merge_when_clause:
 			WHEN MATCHED opt_merge_when_and_condition THEN merge_update
 				{
-					MergeAction *m = makeNode(MergeAction);
+					$5->matched = true;
+					$5->commandType = CMD_UPDATE;
+					$5->condition = $3;
 
-					m->matched = true;
-					m->commandType = CMD_UPDATE;
-					m->condition = $3;
-					m->stmt = $5;
-
-					$$ = (Node *)m;
+					$$ = (Node *) $5;
 				}
 			| WHEN MATCHED opt_merge_when_and_condition THEN merge_delete
 				{
-					MergeAction *m = makeNode(MergeAction);
+					MergeWhenClause *m = makeNode(MergeWhenClause);
 
 					m->matched = true;
 					m->commandType = CMD_DELETE;
 					m->condition = $3;
-					m->stmt = $5;
 
 					$$ = (Node *)m;
 				}
 			| WHEN NOT MATCHED opt_merge_when_and_condition THEN merge_insert
 				{
-					MergeAction *m = makeNode(MergeAction);
+					$6->matched = false;
+					$6->commandType = CMD_INSERT;
+					$6->condition = $4;
 
-					m->matched = false;
-					m->commandType = CMD_INSERT;
-					m->condition = $4;
-					m->stmt = $6;
-
-					$$ = (Node *)m;
+					$$ = (Node *) $6;
 				}
 			| WHEN NOT MATCHED opt_merge_when_and_condition THEN DO NOTHING
 				{
-					MergeAction *m = makeNode(MergeAction);
+					MergeWhenClause *m = makeNode(MergeWhenClause);
 
 					m->matched = false;
 					m->commandType = CMD_NOTHING;
 					m->condition = $4;
-					m->stmt = NULL;
 
 					$$ = (Node *)m;
 				}
@@ -11181,65 +11175,63 @@ opt_merge_when_and_condition:
 			;
 
 merge_delete:
-			DELETE_P
-				{
-					DeleteStmt *n = makeNode(DeleteStmt);
-					$$ = (Node *)n;
-				}
+			DELETE_P 				{ $$ = NULL; }
 			;
 
 merge_update:
 			UPDATE SET set_clause_list
 				{
-					UpdateStmt *n = makeNode(UpdateStmt);
+					MergeWhenClause *n = makeNode(MergeWhenClause);
 					n->targetList = $3;
 
-					$$ = (Node *)n;
+					$$ = n;
 				}
 			;
 
 merge_insert:
-			INSERT values_clause
+			INSERT merge_values_clause
 				{
-					InsertStmt *n = makeNode(InsertStmt);
+					MergeWhenClause *n = makeNode(MergeWhenClause);
 					n->cols = NIL;
-					n->selectStmt = $2;
-
-					$$ = (Node *)n;
+					n->values = $2;
+					$$ = n;
 				}
-			| INSERT OVERRIDING override_kind VALUE_P values_clause
+			| INSERT OVERRIDING override_kind VALUE_P merge_values_clause
 				{
-					InsertStmt *n = makeNode(InsertStmt);
+					MergeWhenClause *n = makeNode(MergeWhenClause);
 					n->cols = NIL;
 					n->override = $3;
-					n->selectStmt = $5;
-
-					$$ = (Node *)n;
+					n->values = $5;
+					$$ = n;
 				}
-			| INSERT '(' insert_column_list ')' values_clause
+			| INSERT '(' insert_column_list ')' merge_values_clause
 				{
-					InsertStmt *n = makeNode(InsertStmt);
+					MergeWhenClause *n = makeNode(MergeWhenClause);
 					n->cols = $3;
-					n->selectStmt = $5;
-
-					$$ = (Node *)n;
+					n->values = $5;
+					$$ = n;
 				}
-			| INSERT '(' insert_column_list ')' OVERRIDING override_kind VALUE_P values_clause
+			| INSERT '(' insert_column_list ')' OVERRIDING override_kind VALUE_P merge_values_clause
 				{
-					InsertStmt *n = makeNode(InsertStmt);
+					MergeWhenClause *n = makeNode(MergeWhenClause);
 					n->cols = $3;
 					n->override = $6;
-					n->selectStmt = $8;
-
-					$$ = (Node *)n;
+					n->values = $8;
+					$$ = n;
 				}
 			| INSERT DEFAULT VALUES
 				{
-					InsertStmt *n = makeNode(InsertStmt);
+					MergeWhenClause *n = makeNode(MergeWhenClause);
 					n->cols = NIL;
-					n->selectStmt = NULL;
+					n->values = NIL;
+					$$ = n;
+				}
+			;
 
-					$$ = (Node *)n;
+merge_values_clause:
+			VALUES '(' expr_list ')'
+				{
+					$$ = $3;
 				}
 			;
 

src/backend/parser/parse_merge.c

@@ -33,8 +33,8 @@
 
 static int transformMergeJoinClause(ParseState *pstate, Node *merge,
 						List **mergeSourceTargetList);
-static void setNamespaceForMergeAction(ParseState *pstate,
-						MergeAction *action);
+static void setNamespaceForMergeWhen(ParseState *pstate,
+						MergeWhenClause *mergeWhenClause);
 static void setNamespaceVisibilityForRTE(List *namespace, RangeTblEntry *rte,
 							 bool rel_visible,
 							 bool cols_visible);
@@ -138,7 +138,7 @@ transformMergeJoinClause(ParseState *pstate, Node *merge,
  * that columns can be referenced unqualified from these relations.
  */
 static void
-setNamespaceForMergeAction(ParseState *pstate, MergeAction *action)
+setNamespaceForMergeWhen(ParseState *pstate, MergeWhenClause *mergeWhenClause)
 {
 	RangeTblEntry *targetRelRTE,
 			   *sourceRelRTE;
@@ -152,7 +152,7 @@ setNamespaceForMergeAction(ParseState *pstate, MergeAction *action)
 	 */
 	sourceRelRTE = rt_fetch(list_length(pstate->p_rtable) - 1, pstate->p_rtable);
 
-	switch (action->commandType)
+	switch (mergeWhenClause->commandType)
 	{
 		case CMD_INSERT:
 
@@ -198,6 +198,7 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 	bool			is_terminal[2];
 	JoinExpr	   *joinexpr;
 	RangeTblEntry  *resultRelRTE, *mergeRelRTE;
+	List		   *mergeActionList;
 
 	/* There can't be any outer WITH to worry about */
 	Assert(pstate->p_ctenamespace == NIL);
@@ -222,43 +223,18 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 	 */
 	is_terminal[0] = false;
 	is_terminal[1] = false;
-	foreach(l, stmt->mergeActionList)
+	foreach(l, stmt->mergeWhenClauses)
 	{
-		MergeAction *action = (MergeAction *) lfirst(l);
-		int		when_type = (action->matched ? 0 : 1);
+		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
+		int		when_type = (mergeWhenClause->matched ? 0 : 1);
 
 		/*
 		 * Collect action types so we can check Target permissions
 		 */
-		switch (action->commandType)
+		switch (mergeWhenClause->commandType)
 		{
 			case CMD_INSERT:
-				{
-					InsertStmt *istmt = (InsertStmt *) action->stmt;
-					SelectStmt *selectStmt = (SelectStmt *) istmt->selectStmt;
-
-					/*
-					 * The grammar allows attaching ORDER BY, LIMIT, FOR
-					 * UPDATE, or WITH to a VALUES clause and also multiple
-					 * VALUES clauses. If we have any of those, ERROR.
-					 */
-					if (selectStmt && (selectStmt->valuesLists == NIL ||
-									   selectStmt->sortClause != NIL ||
-									   selectStmt->limitOffset != NULL ||
-									   selectStmt->limitCount != NULL ||
-									   selectStmt->lockingClause != NIL ||
-									   selectStmt->withClause != NULL))
-						ereport(ERROR,
-								(errcode(ERRCODE_SYNTAX_ERROR),
-								 errmsg("SELECT not allowed in MERGE INSERT statement")));
-
-					if (selectStmt && list_length(selectStmt->valuesLists) > 1)
-						ereport(ERROR,
-								(errcode(ERRCODE_SYNTAX_ERROR),
-								 errmsg("Multiple VALUES clauses not allowed in MERGE INSERT statement")));
-
-					targetPerms |= ACL_INSERT;
-				}
+				targetPerms |= ACL_INSERT;
 				break;
 			case CMD_UPDATE:
 				targetPerms |= ACL_UPDATE;
@@ -275,7 +251,7 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 		/*
 		 * Check for unreachable WHEN clauses
 		 */
-		if (action->condition == NULL)
+		if (mergeWhenClause->condition == NULL)
 			is_terminal[when_type] = true;
 		else if (is_terminal[when_type])
 			ereport(ERROR,
@@ -461,15 +437,20 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 	 * both of those already have RTEs. There is nothing like the EXCLUDED
 	 * pseudo-relation for INSERT ON CONFLICT.
 	 */
-	foreach(l, stmt->mergeActionList)
+	mergeActionList = NIL;
+	foreach(l, stmt->mergeWhenClauses)
 	{
-		MergeAction *action = (MergeAction *) lfirst(l);
+		MergeWhenClause *mergeWhenClause = (MergeWhenClause *) lfirst(l);
+		MergeAction		  *action = makeNode(MergeAction);
+
+		action->commandType = mergeWhenClause->commandType;
+		action->matched = mergeWhenClause->matched;
 
 		/*
 		 * Set namespace for the specific action. This must be done before
 		 * analyzing the WHEN quals and the action targetlisst.
 		 */
-		setNamespaceForMergeAction(pstate, action);
+		setNamespaceForMergeWhen(pstate, mergeWhenClause);
 
 		/*
 		 * Transform the when condition.
@@ -478,7 +459,7 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 		 * are evaluated separately during execution to decide which of the
 		 * WHEN MATCHED or WHEN NOT MATCHED actions to execute.
 		 */
-		action->qual = transformWhereClause(pstate, action->condition,
+		action->qual = transformWhereClause(pstate, mergeWhenClause->condition,
 											EXPR_KIND_MERGE_WHEN_AND, "WHEN");
 
 		/*
@@ -488,8 +469,6 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 		{
 			case CMD_INSERT:
 				{
-					InsertStmt *istmt = (InsertStmt *) action->stmt;
-					SelectStmt *selectStmt = (SelectStmt *) istmt->selectStmt;
 					List	   *exprList = NIL;
 					ListCell   *lc;
 					RangeTblEntry *rte;
@@ -500,13 +479,17 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 
 					pstate->p_is_insert = true;
 
-					icolumns = checkInsertTargets(pstate, istmt->cols, &attrnos);
+					icolumns = checkInsertTargets(pstate,
+												  mergeWhenClause->cols,
+												  &attrnos);
 					Assert(list_length(icolumns) == list_length(attrnos));
 
+					action->override = mergeWhenClause->override;
+
 					/*
 					 * Handle INSERT much like in transformInsertStmt
 					 */
-					if (selectStmt == NULL)
+					if (mergeWhenClause->values == NIL)
 					{
 						/*
 						 * We have INSERT ... DEFAULT VALUES.  We can handle
@@ -525,23 +508,19 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 						 * as the Query's targetlist, with no VALUES RTE.  So
 						 * it works just like a SELECT without any FROM.
 						 */
-						List	   *valuesLists = selectStmt->valuesLists;
-
-						Assert(list_length(valuesLists) == 1);
-						Assert(selectStmt->intoClause == NULL);
 
 						/*
 						 * Do basic expression transformation (same as a ROW()
 						 * expr, but allow SetToDefault at top level)
 						 */
 						exprList = transformExpressionList(pstate,
-														   (List *) linitial(valuesLists),
+														   mergeWhenClause->values,
 														   EXPR_KIND_VALUES_SINGLE,
 														   true);
 
 						/* Prepare row for assignment to target table */
 						exprList = transformInsertRow(pstate, exprList,
-													  istmt->cols,
+													  mergeWhenClause->cols,
 													  icolumns, attrnos,
 													  false);
 					}
@@ -580,10 +559,9 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 				break;
 			case CMD_UPDATE:
 				{
-					UpdateStmt *ustmt = (UpdateStmt *) action->stmt;
-
 					pstate->p_is_insert = false;
-					action->targetList = transformUpdateTargetList(pstate, ustmt->targetList);
+					action->targetList = transformUpdateTargetList(pstate,
+																   mergeWhenClause->targetList);
 				}
 				break;
 			case CMD_DELETE:
@@ -595,9 +573,11 @@ transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
 			default:
 				elog(ERROR, "unknown action in MERGE WHEN clause");
 		}
+
+		mergeActionList = lappend(mergeActionList, action);
 	}
 
-	qry->mergeActionList = stmt->mergeActionList;
+	qry->mergeActionList = mergeActionList;
 
 	/* XXX maybe later */
 	qry->returningList = NULL;

src/backend/rewrite/rewriteHandler.c

@@ -3417,12 +3417,10 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 						break;
 					case CMD_INSERT:
 						{
-							InsertStmt *istmt = (InsertStmt *) action->stmt;
-
 							action->targetList =
 								rewriteTargetListIU(action->targetList,
 													action->commandType,
-													istmt->override,
+													action->override,
 													rt_entry_relation,
 													parsetree->resultRelation,
 													NULL);

src/include/nodes/nodes.h

@@ -269,6 +269,7 @@ typedef enum NodeTag
 	T_RollupData,
 	T_GroupingSetData,
 	T_StatisticExtInfo,
+	T_MergeAction,
 
 	/*
 	 * TAGS FOR MEMORY NODES (memnodes.h)
@@ -310,7 +311,6 @@ typedef enum NodeTag
 	T_DeleteStmt,
 	T_UpdateStmt,
 	T_MergeStmt,
-	T_MergeAction,
 	T_SelectStmt,
 	T_AlterTableStmt,
 	T_AlterTableCmd,
@@ -475,6 +475,7 @@ typedef enum NodeTag
 	T_PartitionRangeDatum,
 	T_PartitionCmd,
 	T_VacuumRelation,
+	T_MergeWhenClause,
 
 	/*
 	 * TAGS FOR REPLICATION GRAMMAR PARSE NODES (replnodes.h)

src/include/nodes/parsenodes.h

@@ -1518,19 +1518,34 @@ typedef struct MergeStmt
 	RangeVar   *relation;			/* target relation to merge into */
 	Node	   *source_relation;	/* source relation */
 	Node	   *join_condition; /* join condition between source and target */
-	List	   *mergeActionList;	/* list of MergeAction(s) */
+	List	   *mergeWhenClauses;	/* list of MergeWhenClause(es) */
 	WithClause *withClause;		/* WITH clause */
 } MergeStmt;
 
-typedef struct MergeAction
+typedef struct MergeWhenClause
 {
 	NodeTag		type;
 	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
-	Node	   *condition;		/* WHEN AND conditions (raw parser) */
-	Node	   *qual;			/* transformed WHEN AND conditions */
 	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
-	Node	   *stmt;			/* T_UpdateStmt etc */
-	List	   *targetList;		/* the target list (of ResTarget) */
+	Node	   *condition;		/* WHEN AND conditions (raw parser) */
+	List	   *targetList;		/* INSERT/UPDATE targetlist */
+	/* the following members are only useful for INSERT action */
+	List	   *cols;			/* optional: names of the target columns */
+	List	   *values;			/* VALUES to INSERT, or NULL */
+	OverridingKind override;	/* OVERRIDING clause */
+} MergeWhenClause;
+
+/*
+ * WHEN [NOT] MATCHED THEN action info
+ */
+typedef struct MergeAction
+{
+	NodeTag     type;
+	bool        matched;        /* true=MATCHED, false=NOT MATCHED */
+	OverridingKind	override;	/* OVERRIDING clause */
+	Node       *qual;           /* transformed WHEN AND conditions */
+	CmdType     commandType;    /* INSERT/UPDATE/DELETE/DO NOTHING */
+	List       *targetList;     /* the target list (of ResTarget) */
 } MergeAction;
 
 /* ----------------------

src/test/regress/expected/merge.out

@@ -90,7 +90,9 @@ USING source AS s
 ON t.tid = s.sid
 WHEN NOT MATCHED THEN
 	INSERT VALUES (1,1), (2,2);
-ERROR:  Multiple VALUES clauses not allowed in MERGE INSERT statement
+ERROR:  syntax error at or near ","
+LINE 5:  INSERT VALUES (1,1), (2,2);
+                            ^
 ;
 -- SELECT query for INSERT
 MERGE INTO target t