At 02:26 PM 9/05/2012, you wrote:

>Thanks for your replay.
>
>If you see null with ibexpert, how come this data can be store in Firebird, since ddl for this column not allow for null value? Could it be a bug in Firebird?

It was stored at some point before the column was changed to NOT NULL. When you do that change, the engine does NOT alter existing data. Thus, you must always make sure that you correct the data *before* you make that change.

>Another strange results when issued this statement
>
>SELECT * FROM M_INT_FRM a
>where a.id_div_lc is null
>
>It will returns 3 result (via flamerobin).

Why is it strange? You have already established that you have nulls stored in this column, from its previous life as nullable.

./heLen