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

On Wed, Aug 11, 2010 at 8:09 AM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> 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.

Ok, I see, so, in the meantime, just add all columns: no big deal, I
was only curious on why.

Thanks for your answer!

Ildefonso.