comparing two tables

Captain Paralytic wrote:
> Cleverbum wrote:
>
> > addinall wrote:
> > > Cleverbum wrote:
> > > > Forgive me if you think the subject is wrong, but I can't quite think
> > > > how to describe my question.
> > > > I just deleted some rows of a table and need to see if there were any
> > > > values in another table linked to the rows I deleted.
> > > > I'm looking for a query that would perform:
> > > > Show all records from table1 where the value in column `album` is not
> > > > contained in the any of the rows in column `uid` of table2
> > > > If that makes no sense let me know and I'll try to re-word it and write
> > > > an example.
> > >
> > > select album from table_1
> > > union
> > > select uid from table_2
> > > where
> > > uid not in
> > > (select album from table_1)
> > >
> > > I think that seems to be what you require.
> > >
> > > If not, sorry! I mis-understood, or I'm just plain
> > > stupid!
> > >
> > > Mark Addinall.
> >
> > That seems closer, what actually seems to do the trick is:
> >
> > SELECT *
> > FROM personal_images
> > WHERE album NOT
> > IN (
> >
> > SELECT uid
> > FROM personal_albums
> > )
>
> This query will produce exactly the asme results as Strawberry's LEFT
> JOIN compare with NULL query.
>
> The difference is that the LEFT join is much much much more efficient,
> especially if there is an appropriate index.
>
> See http://dev.mysql.com/doc/refman/5.0/...ubqueries.html

I'll bare that in mind, I couldn't understand the left join one as well
so found it harder to modify when it came up with an error first time.
Thanks for all your help.
Martin.