Fix oversight in planning of GROUP queries: when an expression is used

as both a GROUP BY item and an output expression, the top-level Group
node should just copy up the evaluated expression value from its input,
rather than re-evaluating the expression.  Aside from any performance
benefit this might offer, this avoids a crash when there is a sub-SELECT
in said expression.

src/backend/optimizer/plan/setrefs.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.68 2000/10/26 21:36:09 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.69 2001/01/09 03:48:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -17,6 +17,7 @@
 
 #include "postgres.h"
 
+#include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/planmain.h"
@@ -270,22 +271,75 @@ set_join_references(Join *join)
  *	  to refer to the tuples returned by its lefttree subplan.
  *
  * This is used for single-input plan types like Agg, Group, Result.
+ *
+ * In most cases, we have to match up individual Vars in the tlist and
+ * qual expressions with elements of the subplan's tlist (which was
+ * generated by flatten_tlist() from these selfsame expressions, so it
+ * should have all the required variables).  There is an important exception,
+ * however: a GROUP BY expression that is also an output expression will
+ * have been pushed into the subplan tlist unflattened.  We want to detect
+ * this case and reference the subplan output directly.  Therefore, check
+ * for equality of the whole tlist expression to any subplan element before
+ * we resort to picking the expression apart for individual Vars.
  */
 static void
 set_uppernode_references(Plan *plan, Index subvarno)
 {
 	Plan	   *subplan = plan->lefttree;
-	List	   *subplanTargetList;
+	List	   *subplanTargetList,
+			   *outputTargetList,
+			   *l;
 
 	if (subplan != NULL)
 		subplanTargetList = subplan->targetlist;
 	else
 		subplanTargetList = NIL;
 
-	plan->targetlist = (List *)
-		replace_vars_with_subplan_refs((Node *) plan->targetlist,
-									   subvarno,
-									   subplanTargetList);
+	outputTargetList = NIL;
+	foreach (l, plan->targetlist)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(l);
+		TargetEntry *subplantle;
+		Node	   *newexpr;
+
+		subplantle = tlistentry_member(tle->expr, subplanTargetList);
+		if (subplantle)
+		{
+			/* Found a matching subplan output expression */
+			Resdom *resdom = subplantle->resdom;
+			Var	   *newvar;
+
+			newvar = makeVar(subvarno,
+							 resdom->resno,
+							 resdom->restype,
+							 resdom->restypmod,
+							 0);
+			/* If we're just copying a simple Var, copy up original info */
+			if (subplantle->expr && IsA(subplantle->expr, Var))
+			{
+				Var	   *subvar = (Var *) subplantle->expr;
+
+				newvar->varnoold = subvar->varnoold;
+				newvar->varoattno = subvar->varoattno;
+			}
+			else
+			{
+				newvar->varnoold = 0;
+				newvar->varoattno = 0;
+			}
+			newexpr = (Node *) newvar;
+		}
+		else
+		{
+			/* No matching expression, so replace individual Vars */
+			newexpr = replace_vars_with_subplan_refs(tle->expr,
+													 subvarno,
+													 subplanTargetList);
+		}
+		outputTargetList = lappend(outputTargetList,
+								   makeTargetEntry(tle->resdom, newexpr));
+	}
+	plan->targetlist = outputTargetList;
 
 	plan->qual = (List *)
 		replace_vars_with_subplan_refs((Node *) plan->qual,

src/backend/optimizer/plan/subselect.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.46 2000/11/21 00:17:59 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.47 2001/01/09 03:48:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -125,6 +125,7 @@ make_subplan(SubLink *slink)
 {
 	SubPlan    *node = makeNode(SubPlan);
 	Query	   *subquery = (Query *) (slink->subselect);
+	Oid			result_type = exprType((Node *) slink);
 	double		tuple_fraction;
 	Plan	   *plan;
 	List	   *lst;
@@ -368,7 +369,7 @@ make_subplan(SubLink *slink)
 		/*
 		 * Make expression of SUBPLAN type
 		 */
-		expr->typeOid = BOOLOID;/* bogus, but we don't really care */
+		expr->typeOid = result_type;
 		expr->opType = SUBPLAN_EXPR;
 		expr->oper = (Node *) node;
 

src/backend/optimizer/util/tlist.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/tlist.c,v 1.47 2000/08/08 15:41:53 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/tlist.c,v 1.48 2001/01/09 03:48:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,7 +18,6 @@
 #include "optimizer/tlist.h"
 #include "optimizer/var.h"
 
-static TargetEntry *tlistentry_member(Node *node, List *targetlist);
 
 /*****************************************************************************
  *	---------- RELATION node target list routines ----------
@@ -29,7 +28,7 @@ static TargetEntry *tlistentry_member(Node *node, List *targetlist);
  *	  Finds the (first) member of the given tlist whose expression is
  *	  equal() to the given expression.	Result is NULL if no such member.
  */
-static TargetEntry *
+TargetEntry *
 tlistentry_member(Node *node, List *targetlist)
 {
 	List	   *temp;

src/include/optimizer/tlist.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: tlist.h,v 1.26 2000/06/08 22:37:51 momjian Exp $
+ * $Id: tlist.h,v 1.27 2001/01/09 03:48:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -16,6 +16,7 @@
 
 #include "nodes/relation.h"
 
+extern TargetEntry *tlistentry_member(Node *node, List *targetlist);
 extern Resdom *tlist_member(Node *node, List *targetlist);
 
 extern void add_var_to_tlist(RelOptInfo *rel, Var *var);