"Guillaume Bog" <guibog@xxxxxxxxx> writes: > I have performance issues if I do the following pseudo-query: > SELECT a, b, (SELECT count(*) FROM t2 WHERE something) AS c > FROM t1 ORDER BY a LIMIT 10; > After some tests, it seems to me that the subquery on t2 is computed for all > rows of t1. Yeah. The SQL specification says that ORDER BY happens after computing the SELECT output-list. In some cases that'll get optimized but you can't count on it. You can probably improve matters by using a sub-select: SELECT a, b, (SELECT count(*) FROM t2 WHERE something) AS c FROM ( SELECT a, b, ... FROM t1 ORDER BY a LIMIT 10 ) ss; regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
