Re: Index Choice Problem

Adam Alkins <adam.alkins@gmail.com> writes:
> SELECT t.topic_id
>             FROM phpbb_topics AS t
>                 WHERE t.forum_id = 71
>                     AND t.topic_id NOT IN (205026, 29046, 144569, 59780, 187424,
> 138635, 184973, 170551, 22419, 181690, 197254, 205130)
>                         ORDER BY t.topic_last_post_time DESC
>                             LIMIT 23 OFFSET 0

If you're using 8.1, you'd probably find that an index on (forum_id,
topic_last_post_time) would work nicely for this.  You could use it
in prior versions too, but you'd have to spell the ORDER BY rather
strangely:
    ORDER BY forum_id desc, topic_last_post_time desc
The reason for this trickery is to get the planner to realize that
the index order matches the ORDER BY ...

            regards, tom lane