How to assign a NULL value with a CASE statement?

Question

I'm trying to assign a NULL value when another field is NULL using a CASE statement.

So far this is what I got:

UPDATE PunchintervalFinal
SET    INDTTIME_LUNCH = (SELECT CASE
                                  WHEN PunchintervalFinal.INDTTIME2 IS NULL THEN
                                  NULL
                                END
                         FROM   PUNCHBRIDGE A
                         WHERE  A.EMPLOYEE = PunchintervalFinal.EMPLOYEE
                                AND A.PUNCHDATE = PunchintervalFinal.PUNCHDATE
                                AND PunchintervalFinal.EMPLOYEE = '500018')  

Answer 1

This should do what you are trying to do:

UPDATE PunchintervalFinal
SET    INDTTIME_LUNCH = NULL
FROM PunchintervalFinal
     INNER JOIN PUNCHBRIDGE A ON A.EMPLOYEE = PunchintervalFinal.EMPLOYEE
WHERE PunchintervalFinal.EMPLOYEE = '500018' 
  AND A.PUNCHDATE = PunchintervalFinal.PUNCHDATE
  AND PunchintervalFinal.INDTTIME2 IS NULL