On Tue, 2004-04-27 at 17:27, Vitaly Belman wrote:
> Hello pgsql-performance,
>
> I discussed the whole subject for some time in DevShed and didn't
> achieve much (as for results). I wonder if any of you guys can help
> out:
>
> http://forums.devshed.com/t136202/s.html
You're taking the wrong approach. Rather than using a select query to
ensure that the book_id is distinct, add a constraint to the table so
that is guaranteed.
CREATE UNIQUE INDEX bv_bookgeneres_unq ON bv_bookgenres(book_id,
genre_id);
Now you can do a simple join (Drop the DISTINCT keyword) and achieve the
same results.
The point is that a book cannot be of a certain genre more than once.
Without the distinct, this should take a matter of a few milliseconds to
execute.
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