>
>The strange result :
>
>Query1=
>Select * from ToDoList
>=> return me 15 records.
>
>When a Query2=
>Select * from ToDoList
>where ToDoList.code in (select codefrom from ToDoListDone);
>=> Return me 2 records
>
>A Query3=
>Select * from ToDoList
>where ToDoList.code not in (select codefrom from ToDoListDone);
>=> return me 0 record !!!!!
>
>Can somebody explain me why not Query1=Query2+Query3 ?

Yes. InterBase is correctly handling three valued logic.
Query1 = Query3 + Query3 + Query4

Query4 =
Select * from ToDoList
where ToDoList.code is null

Good luck,

Ann