--- In firebird-support@yahoogroups.com, Kjell Rilbe
<kjell.rilbe@a...> wrote:

> Not quite. In the second query you're trying to select records where
> RTG.Vahetus is null. I assume that field is a PK and not very likely to
> be null. Anyway, it's not what you want. You want those records from

RTG

> for which no matching Vah record exists. Try again.

Actually RTG.Vahetus is FK and yes, in the second part of the union I
want those records from RTG for which no matching Vah record exists
(so RTG.Vahetus is NULL). Casting NULL as datatype as suggested by
Martijn and Chris seems to work.


ain