Problem with "Not in " operator

I have a table with 2 columns
The cloumn cp_lot_status can be null or 'PL','RE'
The following shows the current data

SQL> SELECT CP_LOT_NUMBER,CP_LOT_STATUS FROM CP_LOTS_GENERATED ;

CP_LOT_NUMBER CP
----- --
203750001
103750001

SQL> SELECT * FROM CP_LOTS_GENERATED WHERE CP_LOT_STATUS NOT IN ('PL','RE') AND
2 CP_LOT_STATUS IS NULL;

no rows selected

SQL> DESC CP_LOTS_GENERATED
Name Null? Type
---------------- --- -------
CP_LOT_NUMBER NOT NULL NUMBER(12)
CP_LOT_STATUS VARCHAR2(2)

So my question is does "Not in " operator not show the null values while doing the above query.IF so what could i do to show the null value rowsNULLs are tricky. They are never equal to, not equal to, IN or NOT IN anything. So this predicate:

WHERE CP_LOT_STATUS NOT IN ('PL','RE')

is neither true nor false when cp_lot_status is NULL - it evaluates to NULL. The query only returns rows where all predicates evaluate to TRUE.

As for what you could do - well, just remove that predicate, it was redundant anyway:

SELECT * FROM CP_LOTS_GENERATED
WHERE CP_LOT_STATUS IS NULL;|||But the values 'PL' and 'RE' may occur at some point of time.....

Originally posted by andrewst
NULLs are tricky. They are never equal to, not equal to, IN or NOT IN anything. So this predicate:

WHERE CP_LOT_STATUS NOT IN ('PL','RE')

is neither true nor false when cp_lot_status is NULL - it evaluates to NULL. The query only returns rows where all predicates evaluate to TRUE.

As for what you could do - well, just remove that predicate, it was redundant anyway:

SELECT * FROM CP_LOTS_GENERATED
WHERE CP_LOT_STATUS IS NULL;|||Well, if they did you would never see them with a query that contained the predicate "AND CP_LOT_STATUS IS NULL".

Maybe what you want is

WHERE (CP_LOT_STATUS NOT IN ('PL','RE')
OR CP_LOT_STATUS IS NULL);|||yeah this worked out

thanx.................

Originally posted by andrewst
Well, if they did you would never see them with a query that contained the predicate "AND CP_LOT_STATUS IS NULL".

Maybe what you want is

WHERE (CP_LOT_STATUS NOT IN ('PL','RE')
OR CP_LOT_STATUS IS NULL);