Elan Ruusamäe <[EMAIL PROTECTED]> [25-05-2007 16:23]: [...] > mysql> select a.category_id,count(*) from album a where exists (select > album_id from image where album_id=a.id) group by 1; > Empty set (0.00 sec)
This query makes little sense and is not ANSI SQL compliant (category_id
not used in aggregate statement or GROUP BY), so both behaviours are
incorrect -- it should return an error.
If you want to count the number of albums in a given category which have
images, that would be the proper query (exists vs join: depending on the
amount of data):
select a.category_id, count(*)
from album a
join image i on i.album_id=a.id
group by a.category_id;
</offtopic>
--
Radosław Zieliński <[EMAIL PROTECTED]>
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