Fix EquivalenceClass code to handle volatile sort expressions in a more

predictable manner; in particular that if you say ORDER BY output-column-ref,
it will in fact sort by that specific column even if there are multiple
syntactic matches.  An example is
	SELECT random() AS a, random() AS b FROM ... ORDER BY b, a;
While the use-case for this might be a bit debatable, it worked as expected
in earlier releases, so we should preserve the behavior for 8.3.  Per my
recent proposal.

While at it, fix convert_subquery_pathkeys() to handle RelabelType stripping
in both directions; it needs this for the same reasons make_sort_from_pathkeys
does.

src/backend/nodes/outfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.315 2007/10/11 18:05:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.316 2007/11/08 21:49:47 tgl Exp $
  *
  * NOTES
  *	  Every node type that can appear in stored rules' parsetrees *must*
@@ -1405,6 +1405,7 @@ _outEquivalenceClass(StringInfo str, EquivalenceClass *node)
 	WRITE_BOOL_FIELD(ec_has_volatile);
 	WRITE_BOOL_FIELD(ec_below_outer_join);
 	WRITE_BOOL_FIELD(ec_broken);
+	WRITE_UINT_FIELD(ec_sortref);
 }
 
 static void

src/backend/optimizer/path/equivclass.c

@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.3 2007/07/07 20:46:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.4 2007/11/08 21:49:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -294,6 +294,7 @@ process_equivalence(PlannerInfo *root, RestrictInfo *restrictinfo,
 		ec->ec_has_volatile = false;
 		ec->ec_below_outer_join = below_outer_join;
 		ec->ec_broken = false;
+		ec->ec_sortref = 0;
 		ec->ec_merged = NULL;
 		em1 = add_eq_member(ec, item1, item1_relids, false, item1_type);
 		em2 = add_eq_member(ec, item2, item2_relids, false, item2_type);
@@ -354,6 +355,9 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
  *	  class it is a member of; if none, build a new single-member
  *	  EquivalenceClass for it.
  *
+ * sortref is the SortGroupRef of the originating SortClause, if any,
+ * or zero if not.
+ *
  * This can be used safely both before and after EquivalenceClass merging;
  * since it never causes merging it does not invalidate any existing ECs
  * or PathKeys.
@@ -367,7 +371,8 @@ EquivalenceClass *
 get_eclass_for_sort_expr(PlannerInfo *root,
 						 Expr *expr,
 						 Oid expr_datatype,
-						 List *opfamilies)
+						 List *opfamilies,
+						 Index sortref)
 {
 	EquivalenceClass *newec;
 	EquivalenceMember *newem;
@@ -382,7 +387,9 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 		EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
 		ListCell   *lc2;
 
-		/* we allow matching to a volatile EC here */
+		/* Never match to a volatile EC */
+		if (cur_ec->ec_has_volatile)
+			continue;
 
 		if (!equal(opfamilies, cur_ec->ec_opfamilies))
 			continue;
@@ -423,6 +430,7 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 	newec->ec_has_volatile = contain_volatile_functions((Node *) expr);
 	newec->ec_below_outer_join = false;
 	newec->ec_broken = false;
+	newec->ec_sortref = sortref;
 	newec->ec_merged = NULL;
 	newem = add_eq_member(newec, expr, pull_varnos((Node *) expr),
 						  false, expr_datatype);

src/backend/optimizer/plan/createplan.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.233 2007/11/08 19:25:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.234 2007/11/08 21:49:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2730,103 +2730,124 @@ make_sort_from_pathkeys(PlannerInfo *root, Plan *lefttree, List *pathkeys,
 	foreach(i, pathkeys)
 	{
 		PathKey	   *pathkey = (PathKey *) lfirst(i);
+		EquivalenceClass *ec = pathkey->pk_eclass;
 		TargetEntry *tle = NULL;
 		Oid			pk_datatype = InvalidOid;
 		Oid			sortop;
 		ListCell   *j;
 
-		/*
-		 * We can sort by any non-constant expression listed in the pathkey's
-		 * EquivalenceClass.  For now, we take the first one that corresponds
-		 * to an available item in the tlist. If there isn't any, use the first
-		 * one that is an expression in the input's vars.  (The non-const
-		 * restriction only matters if the EC is below_outer_join; but if it
-		 * isn't, it won't contain consts anyway, else we'd have discarded
-		 * the pathkey as redundant.)
-		 *
-		 * XXX if we have a choice, is there any way of figuring out which
-		 * might be cheapest to execute?  (For example, int4lt is likely much
-		 * cheaper to execute than numericlt, but both might appear in the
-		 * same equivalence class...)  Not clear that we ever will have an
-		 * interesting choice in practice, so it may not matter.
-		 */
-		foreach(j, pathkey->pk_eclass->ec_members)
+		if (ec->ec_has_volatile)
 		{
-			EquivalenceMember *em = (EquivalenceMember *) lfirst(j);
-
-			if (em->em_is_const || em->em_is_child)
-				continue;
-
-			tle = tlist_member((Node *) em->em_expr, tlist);
-			if (tle)
-			{
-				pk_datatype = em->em_datatype;
-				break;			/* found expr already in tlist */
-			}
-
 			/*
-			 * We can also use it if the pathkey expression is a relabel
-			 * of the tlist entry, or vice versa.  This is needed for
-			 * binary-compatible cases (cf. make_pathkey_from_sortinfo).
-			 * We prefer an exact match, though, so we do the basic
-			 * search first.
+			 * If the pathkey's EquivalenceClass is volatile, then it must
+			 * have come from an ORDER BY clause, and we have to match it to
+			 * that same targetlist entry.
 			 */
-			tle = tlist_member_ignore_relabel((Node *) em->em_expr, tlist);
-			if (tle)
-			{
-				pk_datatype = em->em_datatype;
-				break;			/* found expr already in tlist */
-			}
+			if (ec->ec_sortref == 0)		/* can't happen */
+				elog(ERROR, "volatile EquivalenceClass has no sortref");
+			tle = get_sortgroupref_tle(ec->ec_sortref, tlist);
+			Assert(tle);
+			Assert(list_length(ec->ec_members) == 1);
+			pk_datatype = ((EquivalenceMember *) linitial(ec->ec_members))->em_datatype;
 		}
-		if (!tle)
+		else
 		{
-			/* No matching tlist item; look for a computable expression */
-			Expr   *sortexpr = NULL;
-
-			foreach(j, pathkey->pk_eclass->ec_members)
+			/*
+			 * Otherwise, we can sort by any non-constant expression listed in
+			 * the pathkey's EquivalenceClass.  For now, we take the first one
+			 * that corresponds to an available item in the tlist.  If there
+			 * isn't any, use the first one that is an expression in the
+			 * input's vars.  (The non-const restriction only matters if the
+			 * EC is below_outer_join; but if it isn't, it won't contain
+			 * consts anyway, else we'd have discarded the pathkey as
+			 * redundant.)
+			 *
+			 * XXX if we have a choice, is there any way of figuring out which
+			 * might be cheapest to execute?  (For example, int4lt is likely
+			 * much cheaper to execute than numericlt, but both might appear
+			 * in the same equivalence class...)  Not clear that we ever will
+			 * have an interesting choice in practice, so it may not matter.
+			 */
+			foreach(j, ec->ec_members)
 			{
 				EquivalenceMember *em = (EquivalenceMember *) lfirst(j);
-				List	   *exprvars;
-				ListCell   *k;
 
 				if (em->em_is_const || em->em_is_child)
 					continue;
-				sortexpr = em->em_expr;
-				exprvars = pull_var_clause((Node *) sortexpr, false);
-				foreach(k, exprvars)
+
+				tle = tlist_member((Node *) em->em_expr, tlist);
+				if (tle)
 				{
-					if (!tlist_member_ignore_relabel(lfirst(k), tlist))
-						break;
+					pk_datatype = em->em_datatype;
+					break;			/* found expr already in tlist */
 				}
-				list_free(exprvars);
-				if (!k)
+
+				/*
+				 * We can also use it if the pathkey expression is a relabel
+				 * of the tlist entry, or vice versa.  This is needed for
+				 * binary-compatible cases (cf. make_pathkey_from_sortinfo).
+				 * We prefer an exact match, though, so we do the basic
+				 * search first.
+				 */
+				tle = tlist_member_ignore_relabel((Node *) em->em_expr, tlist);
+				if (tle)
 				{
 					pk_datatype = em->em_datatype;
-					break;		/* found usable expression */
+					break;			/* found expr already in tlist */
 				}
 			}
-			if (!j)
-				elog(ERROR, "could not find pathkey item to sort");
 
-			/*
-			 * Do we need to insert a Result node?
-			 */
-			if (!is_projection_capable_plan(lefttree))
+			if (!tle)
 			{
-				/* copy needed so we don't modify input's tlist below */
-				tlist = copyObject(tlist);
-				lefttree = (Plan *) make_result(root, tlist, NULL, lefttree);
-			}
+				/* No matching tlist item; look for a computable expression */
+				Expr   *sortexpr = NULL;
 
-			/*
-			 * Add resjunk entry to input's tlist
-			 */
-			tle = makeTargetEntry(sortexpr,
-								  list_length(tlist) + 1,
-								  NULL,
-								  true);
-			tlist = lappend(tlist, tle);
-			lefttree->targetlist = tlist;		/* just in case NIL before */
+				foreach(j, ec->ec_members)
+				{
+					EquivalenceMember *em = (EquivalenceMember *) lfirst(j);
+					List	   *exprvars;
+					ListCell   *k;
+
+					if (em->em_is_const || em->em_is_child)
+						continue;
+					sortexpr = em->em_expr;
+					exprvars = pull_var_clause((Node *) sortexpr, false);
+					foreach(k, exprvars)
+					{
+						if (!tlist_member_ignore_relabel(lfirst(k), tlist))
+							break;
+					}
+					list_free(exprvars);
+					if (!k)
+					{
+						pk_datatype = em->em_datatype;
+						break;		/* found usable expression */
+					}
+				}
+				if (!j)
+					elog(ERROR, "could not find pathkey item to sort");
+
+				/*
+				 * Do we need to insert a Result node?
+				 */
+				if (!is_projection_capable_plan(lefttree))
+				{
+					/* copy needed so we don't modify input's tlist below */
+					tlist = copyObject(tlist);
+					lefttree = (Plan *) make_result(root, tlist, NULL,
+													lefttree);
+				}
+
+				/*
+				 * Add resjunk entry to input's tlist
+				 */
+				tle = makeTargetEntry(sortexpr,
+									  list_length(tlist) + 1,
+									  NULL,
+									  true);
+				tlist = lappend(tlist, tle);
+				lefttree->targetlist = tlist;	/* just in case NIL before */
+			}
 		}
 
 		/*

src/backend/optimizer/util/tlist.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.75 2007/11/08 19:25:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/tlist.c,v 1.76 2007/11/08 21:49:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -131,26 +131,22 @@ add_to_flat_tlist(List *tlist, List *vars)
 	return tlist;
 }
 
+
 /*
- * get_sortgroupclause_tle
- *		Find the targetlist entry matching the given SortClause
- *		(or GroupClause) by ressortgroupref, and return it.
- *
- * Because GroupClause is typedef'd as SortClause, either kind of
- * node can be passed without casting.
+ * get_sortgroupref_tle
+ *		Find the targetlist entry matching the given SortGroupRef index,
+ *		and return it.
  */
 TargetEntry *
-get_sortgroupclause_tle(SortClause *sortClause,
-						List *targetList)
+get_sortgroupref_tle(Index sortref, List *targetList)
 {
-	Index		refnumber = sortClause->tleSortGroupRef;
 	ListCell   *l;
 
 	foreach(l, targetList)
 	{
 		TargetEntry *tle = (TargetEntry *) lfirst(l);
 
-		if (tle->ressortgroupref == refnumber)
+		if (tle->ressortgroupref == sortref)
 			return tle;
 	}
 
@@ -158,6 +154,21 @@ get_sortgroupclause_tle(SortClause *sortClause,
 	return NULL;				/* keep compiler quiet */
 }
 
+/*
+ * get_sortgroupclause_tle
+ *		Find the targetlist entry matching the given SortClause
+ *		(or GroupClause) by ressortgroupref, and return it.
+ *
+ * Because GroupClause is typedef'd as SortClause, either kind of
+ * node can be passed without casting.
+ */
+TargetEntry *
+get_sortgroupclause_tle(SortClause *sortClause,
+						List *targetList)
+{
+	return get_sortgroupref_tle(sortClause->tleSortGroupRef, targetList);
+}
+
 /*
  * get_sortgroupclause_expr
  *		Find the targetlist entry matching the given SortClause

src/include/nodes/relation.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.147 2007/10/11 18:05:27 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.148 2007/11/08 21:49:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -449,7 +449,10 @@ typedef struct IndexOptInfo
  * which is a case that can't arise otherwise since clauses containing
  * volatile functions are never considered mergejoinable.  We mark such
  * EquivalenceClasses specially to prevent them from being merged with
- * ordinary EquivalenceClasses.
+ * ordinary EquivalenceClasses.  Also, for volatile expressions we have
+ * to be careful to match the EquivalenceClass to the correct targetlist
+ * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
+ * So we record the SortGroupRef of the originating sort clause.
  *
  * We allow equality clauses appearing below the nullable side of an outer join
  * to form EquivalenceClasses, but these have a slightly different meaning:
@@ -472,6 +475,7 @@ typedef struct EquivalenceClass
 	bool		ec_has_volatile;	/* the (sole) member is a volatile expr */
 	bool		ec_below_outer_join;	/* equivalence applies below an OJ */
 	bool		ec_broken;			/* failed to generate needed clauses? */
+	Index		ec_sortref;			/* originating sortclause label, or 0 */
 	struct EquivalenceClass *ec_merged;		/* set if merged into another EC */
 } EquivalenceClass;
 

src/include/optimizer/paths.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/paths.h,v 1.99 2007/09/26 18:51:51 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/paths.h,v 1.100 2007/11/08 21:49:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -115,7 +115,8 @@ extern void reconsider_outer_join_clauses(PlannerInfo *root);
 extern EquivalenceClass *get_eclass_for_sort_expr(PlannerInfo *root,
 						 Expr *expr,
 						 Oid expr_datatype,
-						 List *opfamilies);
+						 List *opfamilies,
+						 Index sortref);
 extern void generate_base_implied_equalities(PlannerInfo *root);
 extern List *generate_join_implied_equalities(PlannerInfo *root,
 											  RelOptInfo *joinrel,

src/include/optimizer/tlist.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/tlist.h,v 1.46 2007/11/08 19:25:37 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/tlist.h,v 1.47 2007/11/08 21:49:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,6 +23,8 @@ extern TargetEntry *tlist_member_ignore_relabel(Node *node, List *targetlist);
 extern List *flatten_tlist(List *tlist);
 extern List *add_to_flat_tlist(List *tlist, List *vars);
 
+extern TargetEntry *get_sortgroupref_tle(Index sortref,
+						List *targetList);
 extern TargetEntry *get_sortgroupclause_tle(SortClause *sortClause,
 						List *targetList);
 extern Node *get_sortgroupclause_expr(SortClause *sortClause,