8q5tmkyqry(at)sneakemail(dot)com написа:
> Hi,
>
> I have a two tables:
>
> article
> articleID, name, content
>
> tags
> articleID, tag
>
> I want to find all articles that are tagged with "a" but not "b"
>
> how do I do this?
>
> what I'd like to do is:
>
> <wishful thinking>
> select articleID from tags where tag="a"
> SUBTRACT
> select articleID from tags where tab="b"
> </wishful thinking>
>
> how do I do this in real SQL?
Replace "SUBSTRACT" with "EXCEPT"
(http://www.postgresql.org/docs/current/static/sql-select.html#SQL-EXCEPT)
--
Milen A. Radev