SQL 建立临时表进行查询

SELECT
    min (maxrank) as minofmaxrank
FROM
    (SELECT
        max(rank) as maxrank
    FROM
        tbl_core_staff
    WHERE
        st_ymd<=now() AND
        ed_ymd>now() AND
        staff_cd in ('','','','','','','','','','','','','','','','','','','')
    GROUP BY
        staff_cd
    ) t1
SELECT
    min (maxrank) as minofmaxrank
FR