Re: LIMIT and UNION ALL - Mailing list pgsql-performance

Hello


2011/5/18 Dave Johansen <davejohansen@gmail.com>:
> I am using Postgres 8.3.3 and I have a VIEW which is a UNION ALL of two
> tables but when I do a select on the view using a LIMIT, it scans the entire
> tables and takes significantly longer than writing out the query with the
> LIMITs in the sub-queries themselves. Is there a solution to get the view to
> perform like the query with the LIMIT explicitly placed in the sub-queries?
>
> I noticed a similar question in this post
> http://archives.postgresql.org/pgsql-general/2005-06/msg00488.php but I
> wasn't able to find an answer.

maybe

SELECT *
    FROM (SELECT * FROM tab1 LIMIT n) s1
UNION ALL
  SELECT *
    FROM (SELECT * FROM tab2 LIMIT n) s2
LIMIT n

Regards

Pavel Stehule

>
> Thanks,
> Dave