Hi,

select ID, SENDER_ID
from T_BILL
where SENDER_ID not in ( select id from T_CONTACT )

"SENDER_ID" is set 'NULL' in every dataset.
Oracle returns zero datasets, firebird returns the whole table.

As I am not a sql guru, I don't know if this behavior is defined in
sql, but I find it interesant, that the 2 databases act different.

Best regards / Liebe Grüße aus einem kalten Wien
Andre Dostal