On Sat, 12 Jan 2013 02:47:26 +0100 "T. E. Lawrence" <t.e.lawre...@icloud.com> wrote:
> Hello, > > I have a pretty standard query with two tables: > > SELECT table_a.id FROM table_a a, table_b b WHERE ... AND ... AND b.value=...; > > With the last "AND b.value=..." the query is extremely slow (did not wait for > it to end, but more than a minute), because the value column is not indexed > (contains items longer than 8K). You can construct your own home made index, add a new column in table b, with the first 8-16 bytes/chars of b.value, use this column on your query and refine to a complete b.value. Don't forget tocCreate an index for it too. You can keep this column updated with a trigger. Perhaps you can use a partial index for b.value column, i never used that feature so documentation/others can point you how to do it. > However the previous conditions "WHERE ... AND ... AND" should have already > reduced the candidate rows to just a few (table_b contains over 50m rows). > And indeed, removing the last "AND b.value=..." speeds the query to just a > millisecond. > > Is there a way to instruct PostgreSQL to do first the initial "WHERE ... AND > ... AND" and then the last "AND b.value=..." on the (very small) result? > > Thank you and kind regards, > T. --- --- Eduardo Morras <emorr...@yahoo.es> -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
