Re: ORDER BY in UNION query

Thanks Tom it worked.

rgds
Antony Paul


On Mon, 10 Jan 2005 08:39:50 -0500, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Richard Huxton <dev@archonet.com> writes:
> > Antony Paul wrote:
> >> I need to use ORDER BY clause in a UNION query and the Order BY
> >> columns are not included in the SELECT statement. I tried like this
> >>
> >> (select .... from a) UNION (select ..... from b) order by a.ename;
> >>
> >> It says that
> >> ERROR:  Attribute "ename" not found
>
> > The "order by" is applying to the results of the union, not one of the
> > sub-selects. If you want to sort by a value, you'll need to include it
> > in the results list.
>
> You could suppress the order-by fields after the fact:
>
>         SELECT x,y,z FROM
>           ( (SELECT x,y,z,q FROM a)
>             UNION
>             (SELECT x,y,z,q FROM b)
>             ORDER BY q
>           ) ss;
>
> Also, always ask yourself if you really need UNION or if UNION ALL
> is sufficient.  Removing duplicates from a large UNION is *expensive*,
> and all too often a waste of time.
>
>                         regards, tom lane
>