Hi
I have a query that should return a code depending on a postalcode is
between 2 values. If the first postalcode is Null then use the other
postalcode one instead. The 2 postalcodes are in the same table.

SELECT Code FROM Supro, Person
WHERE "if person.Postal1 isNull then use Person.postal2"
BETWEEN Supro.P1 AND Supro.P2
AND person.personid = 6789

This is what I would use in SQL server:
SELECT Code FROM Supro, Person
WHERE
CASE
WHEN person.Postal1 IS NULL THEN Person.postal2
ELSE person.Postal1
END
BETWEEN Supro.P1 AND Supro.P2
AND person.personid = 6789

But since case doesn´t exist in Interbase I don´t know what to
use.
Any idea on how to achieve this?

Thanks
//Jenny