Improve SELECT DISTINCT to consider hash aggregation, as well as sort/uniq,

[postgresql] / src / backend / optimizer / plan / planmain.c

diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index 5e5da6cda4f1bd6eeff833a97ddd3373830375fa..081a7c9cebd1f37615cd42e2a49d3d29b706e42e 100644 (file)
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/plan/planmain.c,v 1.108 2008/08/03 19:10:52 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/plan/planmain.c,v 1.109 2008/08/05 02:43:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -66,9 +66,9 @@
  * PlannerInfo field and not a passed parameter is that the low-level routines
  * in indxpath.c need to see it.)
  *
- * Note: the PlannerInfo node also includes group_pathkeys and sort_pathkeys,
- * which like query_pathkeys need to be canonicalized once the info is
- * available.
+ * Note: the PlannerInfo node also includes group_pathkeys, distinct_pathkeys,
+ * and sort_pathkeys, which like query_pathkeys need to be canonicalized once
+ * the info is available.
  *
  * tuple_fraction is interpreted as follows:
  *       0: expect all tuples to be retrieved (normal case)
@@ -120,6 +120,8 @@ query_planner(PlannerInfo *root, List *tlist,
                                                                                                         root->query_pathkeys);
                root->group_pathkeys = canonicalize_pathkeys(root,
                                                                                                         root->group_pathkeys);
+               root->distinct_pathkeys = canonicalize_pathkeys(root,
+                                                                                                       root->distinct_pathkeys);
                root->sort_pathkeys = canonicalize_pathkeys(root,
                                                                                                        root->sort_pathkeys);
                return;
@@ -237,10 +239,12 @@ query_planner(PlannerInfo *root, List *tlist,
        /*
         * We have completed merging equivalence sets, so it's now possible to
         * convert the requested query_pathkeys to canonical form.      Also
-        * canonicalize the groupClause and sortClause pathkeys for use later.
+        * canonicalize the groupClause, distinctClause and sortClause pathkeys
+        * for use later.
         */
        root->query_pathkeys = canonicalize_pathkeys(root, root->query_pathkeys);
        root->group_pathkeys = canonicalize_pathkeys(root, root->group_pathkeys);
+       root->distinct_pathkeys = canonicalize_pathkeys(root, root->distinct_pathkeys);
        root->sort_pathkeys = canonicalize_pathkeys(root, root->sort_pathkeys);
 
        /*
@@ -286,9 +290,11 @@ query_planner(PlannerInfo *root, List *tlist,
                /*
                 * If both GROUP BY and ORDER BY are specified, we will need two
                 * levels of sort --- and, therefore, certainly need to read all the
-                * tuples --- unless ORDER BY is a subset of GROUP BY.
+                * tuples --- unless ORDER BY is a subset of GROUP BY.  Likewise if
+                * we have both DISTINCT and GROUP BY.
                 */
-               if (!pathkeys_contained_in(root->sort_pathkeys, root->group_pathkeys))
+               if (!pathkeys_contained_in(root->sort_pathkeys, root->group_pathkeys) ||
+                       !pathkeys_contained_in(root->distinct_pathkeys, root->group_pathkeys))
                        tuple_fraction = 0.0;
        }
        else if (parse->hasAggs || root->hasHavingQual)