On Wed, 29 Oct 2003 10:17:24 -0500, Rod Taylor <[EMAIL PROTECTED]> wrote: >On Wed, 2003-10-29 at 09:03, Robert Treat wrote: >> Indexes: entity_watch_map_pkey primary key btree (entity_id, watch_id), >> ewm_entity_id btree (entity_id), >> >> I can't think of why the second index is there, as ISTM there is no >> instance where the first index wouldn't be used in place of the second > >The cost in evaluating the first index will be a little higher
Yes, the actual cost may be a little higher. But the cost estimation might be significantly higher, so there can be border cases where the planner chooses a sequential scan over a multi-column index scan while a single-column index would correctly be recognized as being faster ... Servus Manfred ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
