On 2011-04-09 20:00, David Fetter wrote:
Given the horrors query generators perpetrate, it might be worth dropping provably redundant ORDER BYs on the floor at planning time.
Well, many people often add a secondary sort-key to their SQL for the only purpose of obtainting a consistent result in the corner-cases where the first sort key is ambiguios.
If the first sort-key isn't planned to be supported by an index-scan, then you'll end up calculating the second sortkey for the entire dataset even if you end up doing a "limit 100" at the end. You can only deem it redundant if there is a primary key in front. if you have a primary key in front, where as a fix may be really good in cases where you have a "n_distinct" at or near -1 in pg_stats for the column. Jesper -- Jesper -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
