I have a problem, and would like you input...

I need to evaluate to columns and then base a third column on their
values. But, I need to include NULL values and this statement isn't
working, what am I doing wrong?  Is this possible?

Example:

CASE A1
   WHEN NULL  THEN CASE A2
                                       WHEN NULL THEN 'B1'
                                       ELSE 'B2'
                                       END
   ELSE 'B3'
END AS C1

So based on if A1 is NULL or not, continue to the nested CASE
statement. If A1 is NOT NULL then assign C1 = B3, but if A1 is NULL AND
A2 is NULL then assign C1 = B1, else assign C1 = B2.

Understand?? Confused??

Any help would be greatly appreciated.
Thanks,
Chris