Re: Using count on a join, group by required?

On tis, 2010-08-10 at 22:21 -0430, Jose Ildefonso Camargo Tolosa wrote:
> And it works, it gives me something like:
>
> product_id | name | code | manufacturer_id |
> manufacturer_name | num_serials
> ------------+----------------------+---------------+-----------------+----------------------------+-------------
> 17 | THE product | 1235711131719 | 19 |
> THE product's manufacturer | 5
> 6 | Car Battery 500A 12V | 7591512021575 | 8 |
> Acumuladores Duncan, C.A. | 11
> 1 | Test product 1 | 123456789012 | 1 |
> Test Manufacturer | 6
>
> Which is correct, and exactly what I wanted.
>
> So far, so good. The thing is: the group by clause, I had to add it
> because the parser forced me to, because it complained like this:
>
> ERROR: column "manufacturer.name" must appear in the GROUP BY clause
> or be used in an aggregate function
>
> and I had to include *all* the requested columns on the group by
> clause, can anybody tell me why? or at least point to some doc that
> help me understanding this?

This is fixed in PostgreSQL 9.1devel (*); there you only need to put the
primary key into the GROUP BY clause. Earlier versions didn't know that
that was enough to ensure a deterministic result.

(*) -- It will probably be a bit over a year before that is released.