--- In firebird-support@yahoogroups.com, "johnsparrowuk" wrote:

> Hi Svein,
>
> I didn't know about the restriction on the WHERE clause... I use
>this structure a lot. Are you sure it's not ok to say:
>
> select a.* from a left join b on a.id = b.id where b.id is null

No, I'm not saying I'm sure about that, just that it confuses me and
that I am curious about its use.

Maybe it is the equivalent of what I normally write as

select a.* from a where
not exists(select * from b where a.id = b.id)

> ??? If it's not valid SQL, shouldn't Firebird refuse to accept it?
> Also, if it's not valid to reference the 'outer' side of an outer
> join, does that mean you can't have a WHERE clause at all in a FULL
> OUTER?!?!?!

The database I normally work with has one million rows or more in its
main tables, and I never use FULL OUTER JOIN on them ;o} You may be
right in that OUTER JOINed tables can be used in the where clause, I
might just have misread some advice on this list a while ago (though
I'll continue to put my limiting criteria for the left joined tables
in my JOIN clause until I experience a case where it causes problems).

Set