On Thu, May 12, 2016 at 8:13 AM, Robert Klemme <shortcutter@xxxxxxxxxxxxxx> wrote: > On Mon, May 9, 2016 at 11:41 PM, SoDupuDupu wrote: >> Владимир-3 wrote >>> It seems my quite complex query runs 10 times faster on "some_column >>> LIKE '%test_1' " vs "some_column LIKE 'test_1' " >>> So I just add "%" to the pattern... >> >> Keep in mind then LIKE '%test_1' and LIKE 'test_1' are not equivalent, using >> the % as a prefix to the argument means that the scan only has to confirm >> that the value ends in 'test_1' where forgoing the % entirely means that you >> are essentially saying some_column='test_1'. > > Yes, but wouldn't the latter test be more efficient usually since it > tests against a prefix - at least with a regular index? In theory. But the planner is imperfect, and they will have different estimated selectivities which could easily tip the planner into making a poor choice for the more selective case. Without seeing the plans, it is hard to say much more. Cheers, Jeff -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
