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Repair problem noted by Elphick: make_rels_by_joins failed to handle

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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...
This commit is contained in:
Tom Lane 2000-04-27 18:35:04 +00:00
parent 85a5303877
commit d6eac08f11
1 changed files with 51 additions and 2 deletions
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53
src/backend/optimizer/path/joinrels.c
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@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * 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 void
make_rels_by_joins(Query *root, int level) make_rels_by_joins(Query *root, int level)
{ {
List *first_old_rel = root->join_rel_list;
List *r; List *r;
/* /*
@ -85,7 +86,9 @@ make_rels_by_joins(Query *root, int level)
* Note that if all available join clauses for this rel * Note that if all available join clauses for this rel
* require more than one other rel, we will fail to make any * require more than one other rel, we will fail to make any
* joins against it here. That's OK; it'll be considered by * 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, make_rels_by_clause_joins(root,
old_rel, 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);
}
} }
/* /*