2010/12/8 Tom Lane <tgl@xxxxxxxxxxxxx>: > Shrirang Chitnis <Shrirang.Chitnis@xxxxxxxxxxxxxxx> 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 >> Â Â Â OR contexts.context_key IN >> Â Â Â Â Â(SELECT collection_data.context_key >> Â Â Â Â ÂFROM collection_data >> Â Â Â Â Â 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. ÂYou might consider replacing > this with a UNION of two scans of "contexts". Â(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 > > Â Â Â Â Â Â Â Â Â Â Â Âregards, tom lane > > -- > Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance > -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
