Fix UNION planner datatype issue

66c0185a3 gave the planner the ability to have union child queries
provide the union planner with pre-sorted input so that UNION queries
could be more efficiently implemented using Merge Append.

That commit overlooked checking that the UNION target list and the union
child target list's types all match.  In some corner cases, this could
result in the planner producing sorts using the sort operator of the
top-level UNION's target list type rather than of the union child's
target list's type.  The implications of this range from silently
working correctly, despite using the wrong sort operator all the way up
to a segmentation fault.

Here we fix by adjusting the planner so it makes no attempt to have the
subquery produce pre-sorted results when the data type of the UNION
target list and the types from the subquery target list don't match
exactly.

Backpatch to 17, where 66c0185a3 was introduced.

Reported-by: Jason Smith <dqetool@126.com>
Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us>
Bug: 18764
Discussion: https://postgr.es/m/18764-63ad667ea26e877a%40postgresql.org
Backpatch-through: 17

src/backend/optimizer/plan/planner.c

@@ -8077,7 +8077,10 @@ group_by_has_partkey(RelOptInfo *input_rel,
  * child query's targetlist entries may already have a tleSortGroupRef
  * assigned for other purposes, such as GROUP BYs.  Here we keep the
  * SortGroupClause list in the same order as 'op' groupClauses and just adjust
- * the tleSortGroupRef to reference the TargetEntry's 'ressortgroupref'.
+ * the tleSortGroupRef to reference the TargetEntry's 'ressortgroupref'.  If
+ * any of the columns in the targetlist don't match to the setop's colTypes
+ * then we return an empty list.  This may leave some TLEs with unreferenced
+ * ressortgroupref markings, but that's harmless.
  */
 static List *
 generate_setop_child_grouplist(SetOperationStmt *op, List *targetlist)
@@ -8085,25 +8088,42 @@ generate_setop_child_grouplist(SetOperationStmt *op, List *targetlist)
 	List	   *grouplist = copyObject(op->groupClauses);
 	ListCell   *lg;
 	ListCell   *lt;
+	ListCell   *ct;
 
 	lg = list_head(grouplist);
+	ct = list_head(op->colTypes);
 	foreach(lt, targetlist)
 	{
 		TargetEntry *tle = (TargetEntry *) lfirst(lt);
 		SortGroupClause *sgc;
+		Oid			coltype;
 
 		/* resjunk columns could have sortgrouprefs.  Leave these alone */
 		if (tle->resjunk)
 			continue;
 
-		/* we expect every non-resjunk target to have a SortGroupClause */
+		/*
+		 * We expect every non-resjunk target to have a SortGroupClause and
+		 * colTypes.
+		 */
 		Assert(lg != NULL);
+		Assert(ct != NULL);
 		sgc = (SortGroupClause *) lfirst(lg);
+		coltype = lfirst_oid(ct);
+
+		/* reject if target type isn't the same as the setop target type */
+		if (coltype != exprType((Node *) tle->expr))
+			return NIL;
+
 		lg = lnext(grouplist, lg);
+		ct = lnext(op->colTypes, ct);
 
 		/* assign a tleSortGroupRef, or reuse the existing one */
 		sgc->tleSortGroupRef = assignSortGroupRef(tle, targetlist);
 	}
+
 	Assert(lg == NULL);
+	Assert(ct == NULL);
+
 	return grouplist;
 }