On Fri, Oct 26, 2012 at 10:39 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Rushabh Lathia <rushabh.lat...@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! > Thanks for nice explanation. > > regards, tom lane > -- Rushabh Lathia
