Fix assorted missing logic for GroupingFunc nodes.

The planner needs to treat GroupingFunc like Aggref for many purposes,
in particular with respect to processing of the argument expressions,
which are not to be evaluated at runtime.  A few places hadn't gotten
that memo, notably including subselect.c's processing of outer-level
aggregates.  This resulted in assertion failures or wrong plans for
cases in which a GROUPING() construct references an outer aggregation
level.

Also fix missing special cases for GroupingFunc in cost_qual_eval
(resulting in wrong cost estimates for GROUPING(), although it's
not clear that that would affect plan shapes in practice) and in
ruleutils.c (resulting in excess parentheses in pretty-print mode).

Per bug #17088 from Yaoguang Chen.  Back-patch to all supported
branches.

Richard Guo, Tom Lane

Discussion: https://postgr.es/m/17088-e33882b387de7f5c@postgresql.org

src/backend/nodes/nodeFuncs.c

@@ -736,6 +736,8 @@ expression_returns_set_walker(Node *node, void *context)
 	/* Avoid recursion for some cases that parser checks not to return a set */
 	if (IsA(node, Aggref))
 		return false;
+	if (IsA(node, GroupingFunc))
+		return false;
 	if (IsA(node, WindowFunc))
 		return false;
 

src/backend/optimizer/path/costsize.c

@@ -4492,6 +4492,12 @@ cost_qual_eval_walker(Node *node, cost_qual_eval_context *context)
 		 */
 		return false;			/* don't recurse into children */
 	}
+	else if (IsA(node, GroupingFunc))
+	{
+		/* Treat this as having cost 1 */
+		context->total.per_tuple += cpu_operator_cost;
+		return false;			/* don't recurse into children */
+	}
 	else if (IsA(node, CoerceViaIO))
 	{
 		CoerceViaIO *iocoerce = (CoerceViaIO *) node;

src/backend/optimizer/plan/subselect.c

@@ -356,15 +356,17 @@ build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
 		Node	   *arg = pitem->item;
 
 		/*
-		 * The Var, PlaceHolderVar, or Aggref has already been adjusted to
-		 * have the correct varlevelsup, phlevelsup, or agglevelsup.
+		 * The Var, PlaceHolderVar, Aggref or GroupingFunc has already been
+		 * adjusted to have the correct varlevelsup, phlevelsup, or
+		 * agglevelsup.
 		 *
-		 * If it's a PlaceHolderVar or Aggref, its arguments might contain
-		 * SubLinks, which have not yet been processed (see the comments for
-		 * SS_replace_correlation_vars).  Do that now.
+		 * If it's a PlaceHolderVar, Aggref or GroupingFunc, its arguments
+		 * might contain SubLinks, which have not yet been processed (see the
+		 * comments for SS_replace_correlation_vars).  Do that now.
 		 */
 		if (IsA(arg, PlaceHolderVar) ||
-			IsA(arg, Aggref))
+			IsA(arg, Aggref) ||
+			IsA(arg, GroupingFunc))
 			arg = SS_process_sublinks(root, arg, false);
 
 		splan->parParam = lappend_int(splan->parParam, pitem->paramId);
@@ -1957,10 +1959,11 @@ process_sublinks_mutator(Node *node, process_sublinks_context *context)
 	}
 
 	/*
-	 * Don't recurse into the arguments of an outer PHV or aggregate here. Any
-	 * SubLinks in the arguments have to be dealt with at the outer query
-	 * level; they'll be handled when build_subplan collects the PHV or Aggref
-	 * into the arguments to be passed down to the current subplan.
+	 * Don't recurse into the arguments of an outer PHV, Aggref or
+	 * GroupingFunc here.  Any SubLinks in the arguments have to be dealt with
+	 * at the outer query level; they'll be handled when build_subplan
+	 * collects the PHV, Aggref or GroupingFunc into the arguments to be
+	 * passed down to the current subplan.
 	 */
 	if (IsA(node, PlaceHolderVar))
 	{
@@ -1972,6 +1975,11 @@ process_sublinks_mutator(Node *node, process_sublinks_context *context)
 		if (((Aggref *) node)->agglevelsup > 0)
 			return node;
 	}
+	else if (IsA(node, GroupingFunc))
+	{
+		if (((GroupingFunc *) node)->agglevelsup > 0)
+			return node;
+	}
 
 	/*
 	 * We should never see a SubPlan expression in the input (since this is
@@ -2084,7 +2092,7 @@ SS_identify_outer_params(PlannerInfo *root)
 	outer_params = NULL;
 	for (proot = root->parent_root; proot != NULL; proot = proot->parent_root)
 	{
-		/* Include ordinary Var/PHV/Aggref params */
+		/* Include ordinary Var/PHV/Aggref/GroupingFunc params */
 		foreach(l, proot->plan_params)
 		{
 			PlannerParamItem *pitem = (PlannerParamItem *) lfirst(l);

src/backend/utils/adt/ruleutils.c

@@ -7895,12 +7895,13 @@ get_parameter(Param *param, deparse_context *context)
 		context->varprefix = true;
 
 		/*
-		 * A Param's expansion is typically a Var, Aggref, or upper-level
-		 * Param, which wouldn't need extra parentheses.  Otherwise, insert
-		 * parens to ensure the expression looks atomic.
+		 * A Param's expansion is typically a Var, Aggref, GroupingFunc, or
+		 * upper-level Param, which wouldn't need extra parentheses.
+		 * Otherwise, insert parens to ensure the expression looks atomic.
 		 */
 		need_paren = !(IsA(expr, Var) ||
 					   IsA(expr, Aggref) ||
+					   IsA(expr, GroupingFunc) ||
 					   IsA(expr, Param));
 		if (need_paren)
 			appendStringInfoChar(context->buf, '(');
@@ -8028,6 +8029,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 		case T_NextValueExpr:
 		case T_NullIfExpr:
 		case T_Aggref:
+		case T_GroupingFunc:
 		case T_WindowFunc:
 		case T_FuncExpr:
 			/* function-like: name(..) or name[..] */
@@ -8144,6 +8146,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_XmlExpr: /* own parentheses */
 				case T_NullIfExpr:	/* other separators */
 				case T_Aggref:	/* own parentheses */
+				case T_GroupingFunc:	/* own parentheses */
 				case T_WindowFunc:	/* own parentheses */
 				case T_CaseExpr:	/* other separators */
 					return true;
@@ -8194,6 +8197,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_XmlExpr: /* own parentheses */
 				case T_NullIfExpr:	/* other separators */
 				case T_Aggref:	/* own parentheses */
+				case T_GroupingFunc:	/* own parentheses */
 				case T_WindowFunc:	/* own parentheses */
 				case T_CaseExpr:	/* other separators */
 					return true;

src/test/regress/expected/groupingsets.out

@@ -2040,4 +2040,49 @@ order by a, b, c;
    |   |  
 (11 rows)
 
+-- test handling of outer GroupingFunc within subqueries
+explain (costs off)
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by cube(v1);
+        QUERY PLAN         
+---------------------------
+ MixedAggregate
+   Hash Key: $2
+   Group Key: ()
+   InitPlan 1 (returns $1)
+     ->  Result
+   InitPlan 3 (returns $2)
+     ->  Result
+   ->  Result
+   SubPlan 2
+     ->  Result
+(10 rows)
+
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by cube(v1);
+ grouping 
+----------
+        1
+        0
+(2 rows)
+
+explain (costs off)
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by v1;
+        QUERY PLAN         
+---------------------------
+ GroupAggregate
+   Group Key: $2
+   InitPlan 1 (returns $1)
+     ->  Result
+   InitPlan 3 (returns $2)
+     ->  Result
+   ->  Result
+   SubPlan 2
+     ->  Result
+(9 rows)
+
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by v1;
+ grouping 
+----------
+        0
+(1 row)
+
 -- end

src/test/regress/sql/groupingsets.sql

@@ -555,4 +555,13 @@ from (values (1, 2, 3), (4, null, 6), (7, 8, 9)) as t (a, b, c)
 group by rollup(a, b), rollup(a, c)
 order by a, b, c;
 
+-- test handling of outer GroupingFunc within subqueries
+explain (costs off)
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by cube(v1);
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by cube(v1);
+
+explain (costs off)
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by v1;
+select (select grouping(v1)) from (values ((select 1))) v(v1) group by v1;
+
 -- end