Be a little smarter about qual handling for semi-joins: a qual that mentions

only the outer side can be pushed down rather than having to be evaluated
at the join.

diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 1208262b8e4b83487669900846be9a241479fae9..d1b590d063120ed6c4645e5afc448ed3cac083c8 100644 (file)
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.143 2008/10/21 20:42:53 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.144 2008/10/25 19:51:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -48,6 +48,7 @@ static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
 static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                        bool is_deduced,
                        bool below_outer_join,
+                       JoinType jointype,
                        Relids qualscope,
                        Relids ojscope,
                        Relids outerjoin_nonnullable);
@@ -342,7 +343,7 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
                                                 below_outer_join);
            else
                distribute_qual_to_rels(root, qual,
-                                       false, below_outer_join,
+                                       false, below_outer_join, JOIN_INNER,
                                        *qualscope, NULL, NULL);
        }
    }
@@ -452,7 +453,7 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
                                                 below_outer_join);
            else
                distribute_qual_to_rels(root, qual,
-                                       false, below_outer_join,
+                                       false, below_outer_join, j->jointype,
                                        *qualscope,
                                        ojscope, nonnullable_rels);
        }
@@ -712,6 +713,7 @@ make_outerjoininfo(PlannerInfo *root,
  * 'is_deduced': TRUE if the qual came from implied-equality deduction
  * 'below_outer_join': TRUE if the qual is from a JOIN/ON that is below the
  *     nullable side of a higher-level outer join
+ * 'jointype': type of join the qual is from (JOIN_INNER for a WHERE clause)
  * 'qualscope': set of baserels the qual's syntactic scope covers
  * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
  *     needed to form this join
@@ -728,6 +730,7 @@ static void
 distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                        bool is_deduced,
                        bool below_outer_join,
+                       JoinType jointype,
                        Relids qualscope,
                        Relids ojscope,
                        Relids outerjoin_nonnullable)
@@ -848,11 +851,16 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
        maybe_equivalence = false;
        maybe_outer_join = false;
    }
-   else if (bms_overlap(relids, outerjoin_nonnullable))
+   else if (bms_overlap(relids, outerjoin_nonnullable) &&
+            (jointype != JOIN_SEMI ||
+             bms_nonempty_difference(relids, outerjoin_nonnullable)))
    {
        /*
         * The qual is attached to an outer join and mentions (some of the)
-        * rels on the nonnullable side, so it's not degenerate.
+        * rels on the nonnullable side, so it's not degenerate.  (For a
+        * JOIN_SEMI qual, we consider it non-degenerate only if it mentions
+        * both sides of the join --- if it mentions only one side, it can
+        * be pushed down.)
         *
         * We can't use such a clause to deduce equivalence (the left and
         * right sides might be unequal above the join because one of them has
@@ -1024,7 +1032,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
                                                   restrictinfo);
                return;
            }
-           if (bms_equal(outerjoin_nonnullable, qualscope))
+           if (jointype == JOIN_FULL)
            {
                /* FULL JOIN (above tests cannot match in this case) */
                root->full_join_clauses = lappend(root->full_join_clauses,
@@ -1077,9 +1085,8 @@ distribute_sublink_quals_to_rels(PlannerInfo *root,
        Node   *qual = (Node *) lfirst(l);
 
        distribute_qual_to_rels(root, qual,
-                               false, below_outer_join,
-                               qualscope, ojscope,
-                               fslink->lefthand);
+                               false, below_outer_join, fslink->jointype,
+                               qualscope, ojscope, fslink->lefthand);
    }
 
    /* Now we can add the SpecialJoinInfo to join_info_list */
@@ -1373,7 +1380,7 @@ process_implied_equality(PlannerInfo *root,
     * Push the new clause into all the appropriate restrictinfo lists.
     */
    distribute_qual_to_rels(root, (Node *) clause,
-                           true, below_outer_join,
+                           true, below_outer_join, JOIN_INNER,
                            qualscope, NULL, NULL);
 }