[GENERAL] count distinct and group by

[Szymon Guz]

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;

thanks,
Szymon