[thelist] single select image from each gallery - MySQL
r937
rudy at r937.com
Wed Jul 2 21:35:51 CDT 2008
> Group by seems to work fine, so quickly we forget...
>
> select gallery_id, image_id from gallery, images where
> gallery.gallery_id = images.image_gallery_id group by gallery_id
that works in mysql, but it will fail totally in any other database system,
simply because it's non-standard
mysql lets you put a column into the SELECT clause and leave it out of the
GROUP BY clause
it this column is not one-to-one with the GROUP BY column(s) -- and in this
case it isn't -- then the value will be indeterminate
read about it in the mysql docs under "GROUP BY and HAVING with hidden
fields"
that said...
... it is exactly appropriate for your needs
in this case, you get an indeterminate image_id for each gallery_id
;o)
rudy
http://r937.com/
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