If @FirstName and @LastName are the variables and contain NULL for 'Not Supplied' then
WHERE (@FirstName IS NULL OR @FirstName = FirstName)
AND (@LastName IS NULL OR @LastName = LastName)
or if you want to test in sequence then
WHERE (CASE
WHEN @FirstName IS NOT NULL AND @LastName IS NOT NULL AND @FirstName = FirstName AND @LastName = LastName THEN 1
WHEN @FirstName IS NOT NULL AND @FirstName = FirstName THEN 1
WHEN @LastName IS NOT NULL AND @LastName = LastName THEN 1
ELSE 0
END) = 1
Far away is close at hand in the images of elsewhere.
Anon.