Why do I get different results with this?

SQL Apprentice Question
This is taken from a large but not very complex SQL statement.


,SUM (CASE ELUBECOUPONS.TICKETID WHEN NULL THEN 0 ELSE 1 END)


when I execute the statement with the one above the answer is 0 rows.


If I change that statement to:


,SUM (CASE WHEN ELUBECOUPONS.TICKETID IS NULL THEN 0 ELSE 1 END)


the answer is 624,510 rows


Same database, I only changed this one result column.


I clearly don't understand something about the case statement.

Celko Answers
What is the basic rule about NULLs? They cannot be compared to
anything, even eaqch other! You mean to use the other form of CASE
expression:

SUM (CASE WHEN ElubeCoupons.ticket_nbr IS NULL THEN 0 ELSE 1 END)


Since SUM() drops out NULLs, you could use this with numeric ticket
numbers.


SUM (SIGN (ElubeCoupons.ticket_nbr))


Little data modeling thing; a "_nbr" implies a sequence or other
generating rule for the numeric or pseudo-numeric value. "_id" just
says that the value is unique. That is why we talk about ticket
numbers and not ticket identifiers.