Re: Overhead of union versus union all

On Fri, Jul 10, 2009 at 6:37 PM, Jeff Davis<pgsql@j-davis.com> wrote:
>
> -- foo has a primary key
> SELECT * FROM foo UNION SELECT * FROM foo;
>
> That's logically equivalent to:
>
> SELECT * FROM foo;
>
> But postgresql will add a sort anyway.


Well no, it's equivalent to SELECT DISTINCT * FROM foo;


--
greg
http://mit.edu/~gsstark/resume.pdf