Major revision of sort-node handling: push knowledge of query

sort order down into planner, instead of handling it only at the very top
level of the planner.  This fixes many things.  An explicit sort is now
avoided if there is a cheaper alternative (typically an indexscan) not
only for ORDER BY, but also for the internal sort of GROUP BY.  It works
even when there is no other reason (such as a WHERE condition) to consider
the indexscan.  It works for indexes on functions.  It works for indexes
on functions, backwards.  It's just so cool...

CAUTION: I have changed the representation of SortClause nodes, therefore
THIS UPDATE BREAKS STORED RULES.  You will need to initdb.

1 files changed, 23 insertions, 24 deletions

diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 0cc4780807e..2a9ddfc716a 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/preptlist.c,v 1.29 1999/08/09 03:13:31 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/preptlist.c,v 1.30 1999/08/21 03:49:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -163,7 +163,6 @@ replace_matching_resname(List *new_tlist, List *old_tlist)
 		{
 			TargetEntry *old_tle = (TargetEntry *) lfirst(temp);
 
-			old_tle = lfirst(temp);
 			if (!strcmp(old_tle->resdom->resname,
 						new_tle->resdom->resname))
 			{
@@ -174,6 +173,7 @@ replace_matching_resname(List *new_tlist, List *old_tlist)
 
 		if (matching_old_tl)
 		{
+			/* XXX safe to modify old resdom? */
 			matching_old_tl->resdom->resno = new_tle->resdom->resno;
 			t_list = lappend(t_list, matching_old_tl);
 		}
@@ -197,45 +197,42 @@ replace_matching_resname(List *new_tlist, List *old_tlist)
 	{
 		TargetEntry *old_tle,
 				   *new_tl;
-		Resdom	   *newresno;
 
 		old_tle = lfirst(temp);
 		if (old_tle->resdom->resno < 0)
 		{
-			newresno = (Resdom *) copyObject((Node *) old_tle->resdom);
-			newresno->resno = length(t_list) + 1;
-			newresno->resjunk = true;
-			new_tl = makeTargetEntry(newresno, old_tle->expr);
+			Resdom	   *newresdom;
+
+			newresdom = (Resdom *) copyObject((Node *) old_tle->resdom);
+			newresdom->resno = length(t_list) + 1;
+			newresdom->resjunk = true;
+			new_tl = makeTargetEntry(newresdom, old_tle->expr);
 			t_list = lappend(t_list, new_tl);
 		}
-
 		/*
 		 * Also it is possible that the parser or rewriter added some junk
-		 * attributes to hold GROUP BY expressions which are not part of
+		 * attributes to hold ORDER/GROUP BY expressions which are not part of
 		 * the result attributes. We can simply identify them by looking
-		 * at the resgroupref in the TLE's resdom, which is a unique
-		 * number telling which TLE belongs to which GroupClause.
+		 * at the ressortgroupref in the TLE's resdom, which is a unique
+		 * number telling which TLE belongs to which Sort/GroupClause.
 		 */
-		if (old_tle->resdom->resgroupref > 0)
+		else if (old_tle->resdom->ressortgroupref > 0)
 		{
-			bool		already_there = FALSE;
-			TargetEntry *new_tle;
-			Resdom	   *newresno;
+			bool		already_there = false;
 
 			/*
 			 * Check if the tle is already in the new list
 			 */
 			foreach(i, t_list)
 			{
-				new_tle = (TargetEntry *) lfirst(i);
+				TargetEntry *new_tle = (TargetEntry *) lfirst(i);
 
-				if (new_tle->resdom->resgroupref ==
-					old_tle->resdom->resgroupref)
+				if (new_tle->resdom->ressortgroupref ==
+					old_tle->resdom->ressortgroupref)
 				{
-					already_there = TRUE;
+					already_there = true;
 					break;
 				}
-
 			}
 
 			/*
@@ -243,10 +240,12 @@ replace_matching_resname(List *new_tlist, List *old_tlist)
 			 */
 			if (!already_there)
 			{
-				newresno = (Resdom *) copyObject((Node *) old_tle->resdom);
-				newresno->resno = length(t_list) + 1;
-				newresno->resjunk = true;
-				new_tl = makeTargetEntry(newresno, old_tle->expr);
+				Resdom	   *newresdom;
+
+				newresdom = (Resdom *) copyObject((Node *) old_tle->resdom);
+				newresdom->resno = length(t_list) + 1;
+				newresdom->resjunk = true;
+				new_tl = makeTargetEntry(newresdom, old_tle->expr);
 				t_list = lappend(t_list, new_tl);
 			}
 		}