Repair problem noted by Elphick: make_rels_by_joins failed to handle

cases where joinclauses were present but some joins have to be made
by cartesian-product join anyway.  An example is
SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
Even though all the rels have joinclauses, we must join two of them
in cartesian style before we can use the join clause...

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 09003eb9fa852d5448b8ca94000cc0644a5a70aa..df37c58fc723493bedc992f9d69bd33785cfd97e 100644 (file)
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.44 2000/04/12 17:15:20 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.45 2000/04/27 18:35:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -39,6 +39,7 @@ static RelOptInfo *make_join_rel(Query *root, RelOptInfo *rel1,
 void
 make_rels_by_joins(Query *root, int level)
 {
+       List       *first_old_rel = root->join_rel_list;
        List       *r;
 
        /*
@@ -85,7 +86,9 @@ make_rels_by_joins(Query *root, int level)
                         * Note that if all available join clauses for this rel
                         * require more than one other rel, we will fail to make any
                         * joins against it here.  That's OK; it'll be considered by
-                        * "bushy plan" join code in a higher-level pass.
+                        * "bushy plan" join code in a higher-level pass where we
+                        * have those other rels collected into a join rel.  See also
+                        * the last-ditch case below.
                         */
                        make_rels_by_clause_joins(root,
                                                                          old_rel,
@@ -161,6 +164,52 @@ make_rels_by_joins(Query *root, int level)
                        }
                }
        }
+
+       /*
+        * Last-ditch effort: if we failed to find any usable joins so far,
+        * force a set of cartesian-product joins to be generated.  This
+        * handles the special case where all the available rels have join
+        * clauses but we cannot use any of the joins yet.  An example is
+        *
+        * SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
+        *
+        * The join clause will be usable at level 3, but at level 2 we have
+        * no choice but to make cartesian joins.  We consider only left-sided
+        * and right-sided cartesian joins in this case (no bushy).
+        */
+       if (root->join_rel_list == first_old_rel)
+       {
+               /* This loop is just like the first one, except we always call
+                * make_rels_by_clauseless_joins().
+                */
+               if (level == 2)
+                       r = root->base_rel_list; /* level-1 is base rels */
+               else
+                       r = root->join_rel_list;
+               for (; r != NIL; r = lnext(r))
+               {
+                       RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
+                       int                     old_level = length(old_rel->relids);
+                       List       *other_rels;
+
+                       if (old_level != level - 1)
+                               break;
+
+                       if (level == 2)
+                               other_rels = lnext(r); /* only consider remaining base
+                                                                               * rels */
+                       else
+                               other_rels = root->base_rel_list; /* consider all base rels */
+
+                       make_rels_by_clauseless_joins(root,
+                                                                                 old_rel,
+                                                                                 other_rels);
+               }
+
+               if (root->join_rel_list == first_old_rel)
+                       elog(ERROR, "make_rels_by_joins: failed to build any %d-way joins",
+                                level);
+       }
 }
 
 /*