The expected behavior can be obtained by filtering out the null in
the subquery or by using "not exists" instead of "not in".
Here is an example:
CREATE TEMPORARY TABLE subquerytable (column1 INTEGER);
INSERT INTO subquerytable VALUES(2);
INSERT INTO subquerytable VALUES(NULL);
INSERT INTO subquerytable VALUES(3);
SELECT true WHERE 1 NOT IN (SELECT column1 FROM subquerytable); -- Wrong
SELECT true WHERE 1 NOT IN (SELECT column1 FROM subquerytable WHERE column1
IS NOT NULL); -- Ok
SELECT true WHERE NOT EXISTS(SELECT * FROM subquerytable WHERE 1 =
column1); -- Ok
It's not clear to me why "not exists" and "not in" return a different result
but it must be per SQL spec
as all DBMS I have seen do that (Oracle, SQL Server, MYSQL, ...)
In most queries I have seen column1 is NOT NULL so IN or EXISTS can both be
used safely.
Jean-Pierre Pelletier
e-djuster