MySQL:Finder gentagne navne i min brugertabel

SELECT u.*
FROM cpnc_User u JOIN
(
    SELECT firstName, lastName
    FROM cpnc_User
    GROUP BY firstName, lastName
    HAVING COUNT(*) > 1
) X on X.firstName = u.firstName AND x.lastName = u.lastName
ORDER BY u.firstName, u.lastName

Der er ingen grund til at lave et sammenkædet felt, bare brug de 2 felter separat