On Sat, Oct 14, 2017 at 3:15 AM, Gourav Kumar <gourav1...@gmail.com> wrote: > Why does have_relevant_joinclause() and have_relevant_eclass_joinclause() > return true for all possible joins for the query given below. > Even when they have no join predicate between them. > e.g. join between ss1 & ws3, ss2 & ws3 etc. >
The prologues of those functions and comments within those explain that. /* * have_relevant_joinclause * Detect whether there is a joinclause that involves * the two given relations. * * Note: the joinclause does not have to be evaluable with only these two * relations. This is intentional. For example consider * SELECT * FROM a, b, c WHERE a.x = (b.y + c.z) * If a is much larger than the other tables, it may be worthwhile to * cross-join b and c and then use an inner indexscan on a.x. Therefore * we should consider this joinclause as reason to join b to c, even though * it can't be applied at that join step. */ /* * have_relevant_eclass_joinclause * Detect whether there is an EquivalenceClass that could produce * a joinclause involving the two given relations. * * This is essentially a very cut-down version of * generate_join_implied_equalities(). Note it's OK to occasionally say "yes" * incorrectly. Hence we don't bother with details like whether the lack of a * cross-type operator might prevent the clause from actually being generated. */ May be you want to see whether those comments are applicable in your case and also see how the callers handle the return values. -- Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
