2017-09-12 9:36 GMT+02:00 Frank Millman <fr...@chagford.com>: > Pavel Stehule wrote: > > > > 2017-09-12 8:45 GMT+02:00 Frank Millman <fr...@chagford.com>: > >> I am using 9.4.4 on Fedora 22. >> >> I am experimenting with optimising a SQL statement. One version uses 4 >> LEFT JOIN’s and a 5-way CASE statement in the body. The second moves the >> filtering into the JOIN section, and I end up with 16 LEFT JOIN’s and no >> CASE statements. >> >> My test involves selecting a single row. Both versions work. The first >> version takes 0.06 seconds. The second takes 0.23 seconds. On further >> experimentation, the time for the second one seems to taken in setting up >> the joins, because if I omit selecting anything from the joined tables, it >> still takes 0.23 seconds. >> > > > > please send result of explain analyze > > > > you can experimentally try increase FROM_COLLAPSE_LIMIT to some higher > number 14 maybe 16 > > > I tried increasing FROM_COLLAPSE_LIMIT, but it made no difference. > > I have attached files containing my SQL command, and the results of > EXPLAIN ANALYSE >
please use https://explain.depesz.com/ for both plans (slow, fast) Regards Pavel > > Frank > > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general > >
