On Fri, Oct 26, 2012 at 10:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Rushabh Lathia <rushabh.lathia@gmail.com> writes: > *-- Hitting all the partition table* > postgres=# explain select a , ( select city_id from measurement where *logdate > = test.b and logdate = '2006-02-02')* xyz from test;
Hm. What's happening here is that you get an equivalence class containing logdate, test.b, and '2006-02-02', where test.b is actually a Param supplied from the outer query level. So the equivclass.c machinery considers that both test.b and '2006-02-02' are constants, and it just picks the first one to construct derived equalities from. So what comes out is "test.b = logdate and test.b = '2006-02-02'", and neither of those can be used by the constraint-exclusion machinery to prove that some partitions of "measurement" can be skipped.
What we need is to teach generate_base_implied_equalities_const() to prefer an actual constant to pseudo-constants. Will fix, thanks for the example!
