Re: count distinct and group by

On Thu, May 7, 2015 at 12:23 PM, Szymon Guz <mabewlun(at)gmail(dot)com> wrote:

> Hi,
> I'm not sure why there is a reason for such behaviour.
>
> For this table:
>
> create table bg(id serial primary key, t text);
>
> This works:
>
> select count(id) from bg;
>
> This works:
>
> select count(distinct id) from bg;
>
> And this doesn't:
>
> select count(distinct id) from bg order by id;
> ERROR: column "bg.id" must appear in the GROUP BY clause or be used in
> an aggregate function
> LINE 1: select count(distinct id) from bg order by id;
>
>
There is no "id" column in the returned dataset to order by. You are just
returning one value, how would it be ordered? (and that row has a column
named "count" - but you can alias it to SELECT count(distinct id) AS id
FROM bg ORDER BY id - it just makes no sense to order a single row..

--
Magnus Hagander
Me: http://www.hagander.net/
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