> What value must it have? Add a default clause to this statement. Or add
> the field as nullable, populate with data and then alter to NOT NULL.

I have tried to add field as nullable, then tried to alter to not null.

UPDATE TMP_RPT SET ID1 = '5'; Commit;
(This statement is OK)
 

UPDATE RDB$RELATION_FIELDS SET RDB$NULL_FLAG = 1
WHERE RDB$FIELD_NAME = 'ID1' AND RDB$RELATION_NAME = 'TMP_RPT';
(This statement raised an error, FB 3.0 doesn't allow SysDBA user to change System table)

Best regards,
Anto