Stačí použít logiku AND/OR, např.
SELECT *
FROM Customers
WHERE ((Firstname IS NULL AND @firstname IS NULL) OR Firstname = @firstname)
AND ((Lastname IS NULL AND @lastname IS NULL) OR Lastname = @lastname);
Stačí použít logiku AND/OR, např.
SELECT *
FROM Customers
WHERE ((Firstname IS NULL AND @firstname IS NULL) OR Firstname = @firstname)
AND ((Lastname IS NULL AND @lastname IS NULL) OR Lastname = @lastname);