In SQL, how do I allow for nulls in the parameter?

Question

I have what seems to be a really easy SQL query I can't figure out and its driving me nuts. This is SQL 2008. Basically, there is a status field where the can pick "pending", "satisfied" or all. If they send in "pending" or "satisfied" there's no problem. But when they pick all I'm having problems. Mostly because I can't figure out how to get the records where this field is null to show up (because it has to be 'is null' instead of '= null'. (This is the way the data will come over; I have no control over that.)

The code I've been using does not work for nulls.

SELECT * FROM Payment_Table where Payment.Status_code = @status_id

Answer 1

You can try

SELECT Col1, Col2,...,Coln --Required Columns
FROM Payment_Table 
where (Payment.Status_code = @status_id OR @status_id IS NULL)

Answer 2

Try:

SELECT * 
FROM Payment_Table 
WHERE Payment.Status_code = ISNULL(@status_id, Status_code)

This will return all payments.