Teach convert_subquery_pathkeys() to handle the case where the

subquery's pathkey is a RelabelType applied to something that appears
in the subquery's output; for example where the subquery returns a
varchar Var and the sort order is shown as that Var coerced to text.
This comes up because varchar doesn't have its own sort operator.
Per example from Peter Hardman.

diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 23bab20..fb5d382 100644 (file)
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.77 2006/07/14 14:52:20 momjian Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.78 2006/08/17 17:02:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1059,39 +1059,73 @@ convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel,
                {
                        PathKeyItem *sub_item = (PathKeyItem *) lfirst(j);
                        Node       *sub_key = sub_item->key;
+                       Expr       *rtarg;
                        ListCell   *k;
 
+                       /*
+                        * We handle two cases: the sub_pathkey key can be either an exact
+                        * match for a targetlist entry, or a RelabelType of a targetlist
+                        * entry.  (The latter case is worth extra code because it arises
+                        * frequently in connection with varchar fields.)
+                        */
+                       if (IsA(sub_key, RelabelType))
+                               rtarg = ((RelabelType *) sub_key)->arg;
+                       else
+                               rtarg = NULL;
+
                        foreach(k, sub_tlist)
                        {
                                TargetEntry *tle = (TargetEntry *) lfirst(k);
+                               Node       *outer_expr;
+                               PathKeyItem *outer_item;
+                               int                     score;
 
-                               if (!tle->resjunk &&
-                                       equal(tle->expr, sub_key))
+                               /* resjunk items aren't visible to outer query */
+                               if (tle->resjunk)
+                                       continue;
+
+                               if (equal(tle->expr, sub_key))
                                {
-                                       /* Found a representation for this sub_key */
-                                       Var                *outer_var;
-                                       PathKeyItem *outer_item;
-                                       int                     score;
-
-                                       outer_var = makeVar(rel->relid,
-                                                                               tle->resno,
-                                                                               exprType((Node *) tle->expr),
-                                                                               exprTypmod((Node *) tle->expr),
-                                                                               0);
-                                       outer_item = makePathKeyItem((Node *) outer_var,
-                                                                                                sub_item->sortop,
-                                                                                                true);
-                                       /* score = # of mergejoin peers */
-                                       score = count_canonical_peers(root, outer_item);
-                                       /* +1 if it matches the proper query_pathkeys item */
-                                       if (retvallen < outer_query_keys &&
-                                               list_member(list_nth(root->query_pathkeys, retvallen), outer_item))
-                                               score++;
-                                       if (score > best_score)
-                                       {
-                                               best_item = outer_item;
-                                               best_score = score;
-                                       }
+                                       /* Exact match */
+                                       outer_expr = (Node *)
+                                               makeVar(rel->relid,
+                                                               tle->resno,
+                                                               exprType((Node *) tle->expr),
+                                                               exprTypmod((Node *) tle->expr),
+                                                               0);
+                               }
+                               else if (rtarg && equal(tle->expr, rtarg))
+                               {
+                                       /* Match after discarding RelabelType */
+                                       outer_expr = (Node *)
+                                               makeVar(rel->relid,
+                                                               tle->resno,
+                                                               exprType((Node *) tle->expr),
+                                                               exprTypmod((Node *) tle->expr),
+                                                               0);
+                                       outer_expr = (Node *)
+                                               makeRelabelType((Expr *) outer_expr,
+                                                                               ((RelabelType *) sub_key)->resulttype,
+                                                                               ((RelabelType *) sub_key)->resulttypmod,
+                                                                               ((RelabelType *) sub_key)->relabelformat);
+                               }
+                               else
+                                       continue;
+
+                               /* Found a representation for this sub_key */
+                               outer_item = makePathKeyItem(outer_expr,
+                                                                                        sub_item->sortop,
+                                                                                        true);
+                               /* score = # of mergejoin peers */
+                               score = count_canonical_peers(root, outer_item);
+                               /* +1 if it matches the proper query_pathkeys item */
+                               if (retvallen < outer_query_keys &&
+                                       list_member(list_nth(root->query_pathkeys, retvallen), outer_item))
+                                       score++;
+                               if (score > best_score)
+                               {
+                                       best_item = outer_item;
+                                       best_score = score;
                                }
                        }
                }