Tom Lane wrote: > Rikard Pavelic <rikard.pave...@zg.htnet.hr> writes: > >> It would be great if Postgres could rewrite this query >> > > AFAICS those queries are not going to produce the same results, > so Postgres would be 100% incorrect to rewrite it like that for you. > > (If they do produce the same results, it would depend on a bunch > of assumptions you have not stated.) > > regards, tom lane >
Can I try again? :) How hard would it be to teach the planner about preserving uniqueness of relations in subqueries? And using that information to remove unnecessary self joins on unique sets? I can try to rewrite some queries to test it on real data for how much gain it would provide. Regards, Rikard -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
