=?ISO-8859-2?Q?Sz=FBcs_G=E1bor?= <[EMAIL PROTECTED]> writes: > Create a table with (at least) two fields, say i and o. > Create three indexes on (i), (o), (i,o) > Insert enough rows to test. > Try to replace min/max aggregates with indexable queries such as:
> SELECT o FROM t WHERE i = 1 ORDER BY o LIMIT 1; > Problem #1: This tends to use one of the single-column indexes (depending on > the frequency of the indexed element), not the two-column index. Also, I'm > not perfectly sure but maybe the planner is right. Why? To get the planner to use the double-column index, you have to use an ORDER BY that matches the index, eg SELECT o FROM t WHERE i = 1 ORDER BY i,o LIMIT 1; regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org