2010/12/8 Tom Lane <t...@sss.pgh.pa.us>: > Shrirang Chitnis <shrirang.chit...@hovservices.com> writes: >> Bryce, >> The two queries are different: > > I suspect the second one is a typo and not what he really wanted. > >> WHERE (contexts.parent_key = 392210 >> OR contexts.context_key IN >> (SELECT collection_data.context_key >> FROM collection_data >> WHERE collection_data.collection_context_key = 392210) > > The only really effective way the planner knows to optimize an > "IN (sub-SELECT)" is to turn it into a semi-join, which is not possible > here because of the unrelated OR clause. You might consider replacing > this with a UNION of two scans of "contexts". (And yes, I know it'd be > nicer if the planner did that for you.)
I remeber a similar case - 9 years ago. slow variant: WHERE pk = C1 OR pk IN (SELECT .. FROM .. WHERE some = C2) I had to rewrite to form WHERE pk IN (SELECT .. FROM WHERE some = C2 UNION ALL SELECT C1) Regards Pavel Stehule > > regards, tom lane > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance > -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
