sql 行数据找出最大的及所有数据最大的

SELECT @charges=ISNULL(MAX(a.maxcharge), 0.00) FROM(
        SELECT (SELECT MAX(maxcharge)
        FROM(VALUES(ilongcharge),(iwidthcharge),(iheightcharge),(iweightcharge ),(ivolumecharge))
        AS maxcharge(maxcharge))AS maxcharge
        FROM @temp) a