Support data-modifying commands (INSERT/UPDATE/DELETE) in WITH.

This patch implements data-modifying WITH queries according to the
semantics that the updates all happen with the same command counter value,
and in an unspecified order.  Therefore one WITH clause can't see the
effects of another, nor can the outer query see the effects other than
through the RETURNING values.  And attempts to do conflicting updates will
have unpredictable results.  We'll need to document all that.

This commit just fixes the code; documentation updates are waiting on
author.

Marko Tiikkaja and Hitoshi Harada

src/backend/optimizer/plan/createplan.c

@@ -4284,7 +4284,8 @@ make_result(PlannerInfo *root,
  * to make it look better sometime.
  */
 ModifyTable *
-make_modifytable(CmdType operation, List *resultRelations,
+make_modifytable(CmdType operation, bool canSetTag,
+				 List *resultRelations,
 				 List *subplans, List *returningLists,
 				 List *rowMarks, int epqParam)
 {
@@ -4334,7 +4335,9 @@ make_modifytable(CmdType operation, List *resultRelations,
 		node->plan.targetlist = NIL;
 
 	node->operation = operation;
+	node->canSetTag = canSetTag;
 	node->resultRelations = resultRelations;
+	node->resultRelIndex = -1;	/* will be set correctly in setrefs.c */
 	node->plans = subplans;
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;

src/backend/optimizer/plan/planner.c

@@ -163,6 +163,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	glob->rewindPlanIDs = NULL;
 	glob->finalrtable = NIL;
 	glob->finalrowmarks = NIL;
+	glob->resultRelations = NIL;
 	glob->relationOids = NIL;
 	glob->invalItems = NIL;
 	glob->lastPHId = 0;
@@ -214,6 +215,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	/* final cleanup of the plan */
 	Assert(glob->finalrtable == NIL);
 	Assert(glob->finalrowmarks == NIL);
+	Assert(glob->resultRelations == NIL);
 	top_plan = set_plan_references(glob, top_plan,
 								   root->parse->rtable,
 								   root->rowMarks);
@@ -239,11 +241,12 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 
 	result->commandType = parse->commandType;
 	result->hasReturning = (parse->returningList != NIL);
+	result->hasModifyingCTE = parse->hasModifyingCTE;
 	result->canSetTag = parse->canSetTag;
 	result->transientPlan = glob->transientPlan;
 	result->planTree = top_plan;
 	result->rtable = glob->finalrtable;
-	result->resultRelations = root->resultRelations;
+	result->resultRelations = glob->resultRelations;
 	result->utilityStmt = parse->utilityStmt;
 	result->intoClause = parse->intoClause;
 	result->subplans = glob->subplans;
@@ -571,7 +574,8 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 				rowMarks = root->rowMarks;
 
 			plan = (Plan *) make_modifytable(parse->commandType,
-										   copyObject(root->resultRelations),
+											 parse->canSetTag,
+											 list_make1_int(parse->resultRelation),
 											 list_make1(plan),
 											 returningLists,
 											 rowMarks,
@@ -787,7 +791,7 @@ inheritance_planner(PlannerInfo *root)
 		/* Make sure any initplans from this rel get into the outer list */
 		root->init_plans = list_concat(root->init_plans, subroot.init_plans);
 
-		/* Build target-relations list for the executor */
+		/* Build list of target-relation RT indexes */
 		resultRelations = lappend_int(resultRelations, appinfo->child_relid);
 
 		/* Build list of per-relation RETURNING targetlists */
@@ -803,8 +807,6 @@ inheritance_planner(PlannerInfo *root)
 		}
 	}
 
-	root->resultRelations = resultRelations;
-
 	/* Mark result as unordered (probably unnecessary) */
 	root->query_pathkeys = NIL;
 
@@ -814,7 +816,6 @@ inheritance_planner(PlannerInfo *root)
 	 */
 	if (subplans == NIL)
 	{
-		root->resultRelations = list_make1_int(parentRTindex);
 		/* although dummy, it must have a valid tlist for executor */
 		tlist = preprocess_targetlist(root, parse->targetList);
 		return (Plan *) make_result(root,
@@ -849,7 +850,8 @@ inheritance_planner(PlannerInfo *root)
 
 	/* And last, tack on a ModifyTable node to do the UPDATE/DELETE work */
 	return (Plan *) make_modifytable(parse->commandType,
-									 copyObject(root->resultRelations),
+									 parse->canSetTag,
+									 resultRelations,
 									 subplans,
 									 returningLists,
 									 rowMarks,
@@ -1725,12 +1727,6 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 										  count_est);
 	}
 
-	/* Compute result-relations list if needed */
-	if (parse->resultRelation)
-		root->resultRelations = list_make1_int(parse->resultRelation);
-	else
-		root->resultRelations = NIL;
-
 	/*
 	 * Return the actual output ordering in query_pathkeys for possible use by
 	 * an outer query level.

src/backend/optimizer/plan/setrefs.c

@@ -173,8 +173,9 @@ static bool extract_query_dependencies_walker(Node *node,
  * The return value is normally the same Plan node passed in, but can be
  * different when the passed-in Plan is a SubqueryScan we decide isn't needed.
  *
- * The flattened rangetable entries are appended to glob->finalrtable,
- * and we also append rowmarks entries to glob->finalrowmarks.
+ * The flattened rangetable entries are appended to glob->finalrtable.
+ * Also, rowmarks entries are appended to glob->finalrowmarks, and the
+ * RT indexes of ModifyTable result relations to glob->resultRelations.
  * Plan dependencies are appended to glob->relationOids (for relations)
  * and glob->invalItems (for everything else).
  *
@@ -552,6 +553,17 @@ set_plan_refs(PlannerGlobal *glob, Plan *plan, int rtoffset)
 											  (Plan *) lfirst(l),
 											  rtoffset);
 				}
+
+				/*
+				 * Append this ModifyTable node's final result relation RT
+				 * index(es) to the global list for the plan, and set its
+				 * resultRelIndex to reflect their starting position in the
+				 * global list.
+				 */
+				splan->resultRelIndex = list_length(glob->resultRelations);
+				glob->resultRelations =
+					list_concat(glob->resultRelations,
+								list_copy(splan->resultRelations));
 			}
 			break;
 		case T_Append:

src/backend/optimizer/plan/subselect.c

@@ -930,6 +930,7 @@ SS_process_ctes(PlannerInfo *root)
 	foreach(lc, root->parse->cteList)
 	{
 		CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
+		CmdType		cmdType = ((Query *) cte->ctequery)->commandType;
 		Query	   *subquery;
 		Plan	   *plan;
 		PlannerInfo *subroot;
@@ -939,9 +940,9 @@ SS_process_ctes(PlannerInfo *root)
 		Param	   *prm;
 
 		/*
-		 * Ignore CTEs that are not actually referenced anywhere.
+		 * Ignore SELECT CTEs that are not actually referenced anywhere.
 		 */
-		if (cte->cterefcount == 0)
+		if (cte->cterefcount == 0 && cmdType == CMD_SELECT)
 		{
 			/* Make a dummy entry in cte_plan_ids */
 			root->cte_plan_ids = lappend_int(root->cte_plan_ids, -1);
@@ -1332,14 +1333,16 @@ simplify_EXISTS_query(Query *query)
 {
 	/*
 	 * We don't try to simplify at all if the query uses set operations,
-	 * aggregates, HAVING, LIMIT/OFFSET, or FOR UPDATE/SHARE; none of these
-	 * seem likely in normal usage and their possible effects are complex.
+	 * aggregates, modifying CTEs, HAVING, LIMIT/OFFSET, or FOR UPDATE/SHARE;
+	 * none of these seem likely in normal usage and their possible effects
+	 * are complex.
 	 */
 	if (query->commandType != CMD_SELECT ||
 		query->intoClause ||
 		query->setOperations ||
 		query->hasAggs ||
 		query->hasWindowFuncs ||
+		query->hasModifyingCTE ||
 		query->havingQual ||
 		query->limitOffset ||
 		query->limitCount ||