WHERE IS NULL, IS NOT NULL or NO WHERE clause depending on SQL Server parameter value

Question

I have a stored procedure in SQL Server 2000 that performs a search based on parameter values. For one of the parameters passed in, I need a different WHERE cla

Answer 1

Here is how you can solve this using a single WHERE clause:

WHERE (@myParm = value1 AND MyColumn IS NULL)
OR  (@myParm = value2 AND MyColumn IS NOT NULL)
OR  (@myParm = value3)

A naïve usage of the CASE statement does not work, by this I mean the following:

SELECT Field1, Field2 FROM MyTable
WHERE CASE @myParam
    WHEN value1 THEN MyColumn IS NULL
    WHEN value2 THEN MyColumn IS NOT NULL
    WHEN value3 THEN TRUE
END

It is possible to solve this using a case statement, see onedaywhen's answer