Re: Speed difference between select ... union select ... and select from partitioned_table - Mailing list pgsql-performance

On Fri, 2007-10-26 at 16:37 -0400, Pablo Alcaraz wrote:
> Hi List!
>
> I executed 2 equivalents queries. The first one uses a union structure.
> The second uses a partitioned table. The tables are the same with 30
> millions of rows each one and the returned rows are the same.
>
> But the union query perform faster than the partitioned query.
>

I think you mean to use UNION ALL here. UNION forces a DISTINCT, which
results in a sort operation. What surprises me is that the UNION is
actually faster than the partitioning using inheritance.

I suspect it has something to do with the GROUP BYs, but we won't know
until you post EXPLAIN ANALYZE results.

    Regards,
    Jeff Davis