Index: src/backend/optimizer/path/equivclass.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/optimizer/path/equivclass.c,v
retrieving revision 1.9
diff -c -r1.9 equivclass.c
*** src/backend/optimizer/path/equivclass.c	9 Jan 2008 20:42:27 -0000	1.9
--- src/backend/optimizer/path/equivclass.c	27 Mar 2008 18:25:23 -0000
***************
*** 1639,1644 ****
--- 1639,1682 ----
  
  
  /*
+  * mutate_eclass_expressions
+  *	  Apply an expression tree mutator to all expressions stored in
+  *	  equivalence classes.
+  *
+  * This is a bit of a hack ... it's currently needed only by planagg.c,
+  * which needs to do a global search-and-replace of MIN/MAX Aggrefs
+  * after eclasses are already set up.  Without changing the eclasses too,
+  * subsequent matching of ORDER BY clauses would fail.
+  *
+  * Note that we assume the mutation won't affect relation membership or any
+  * other properties we keep track of (which is a bit bogus, but by the time
+  * planagg.c runs, it no longer matters).  Also we must be called in the
+  * main planner memory context.
+  */
+ void
+ mutate_eclass_expressions(PlannerInfo *root,
+ 						  Node *(*mutator) (),
+ 						  void *context)
+ {
+ 	ListCell   *lc1;
+ 
+ 	foreach(lc1, root->eq_classes)
+ 	{
+ 		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
+ 		ListCell   *lc2;
+ 
+ 		foreach(lc2, cur_ec->ec_members)
+ 		{
+ 			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
+ 
+ 			cur_em->em_expr = (Expr *)
+ 				mutator((Node *) cur_em->em_expr, context);
+ 		}
+ 	}
+ }
+ 
+ 
+ /*
   * find_eclass_clauses_for_index_join
   *	  Create joinclauses usable for a nestloop-with-inner-indexscan
   *	  scanning the given inner rel with the specified set of outer rels.
Index: src/backend/optimizer/plan/planagg.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/optimizer/plan/planagg.c,v
retrieving revision 1.36
diff -c -r1.36 planagg.c
*** src/backend/optimizer/plan/planagg.c	1 Jan 2008 19:45:50 -0000	1.36
--- src/backend/optimizer/plan/planagg.c	27 Mar 2008 18:25:23 -0000
***************
*** 188,193 ****
--- 188,201 ----
  											 &aggs_list);
  
  	/*
+ 	 * We have to replace Aggrefs with Params in equivalence classes too,
+ 	 * else ORDER BY or DISTINCT on an optimized aggregate will fail.
+ 	 */
+ 	mutate_eclass_expressions(root,
+ 							  replace_aggs_with_params_mutator,
+ 							  &aggs_list);
+ 
+ 	/*
  	 * Generate the output plan --- basically just a Result
  	 */
  	plan = (Plan *) make_result(root, tlist, hqual, NULL);
Index: src/include/optimizer/paths.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/optimizer/paths.h,v
retrieving revision 1.103
diff -c -r1.103 paths.h
*** src/include/optimizer/paths.h	1 Jan 2008 19:45:58 -0000	1.103
--- src/include/optimizer/paths.h	27 Mar 2008 18:25:23 -0000
***************
*** 127,132 ****
--- 127,135 ----
  						   AppendRelInfo *appinfo,
  						   RelOptInfo *parent_rel,
  						   RelOptInfo *child_rel);
+ extern void mutate_eclass_expressions(PlannerInfo *root,
+ 									  Node *(*mutator) (),
+ 									  void *context);
  extern List *find_eclass_clauses_for_index_join(PlannerInfo *root,
  								   RelOptInfo *rel,
  								   Relids outer_relids);