mysql不同字符集转换比较

SELECT t1.id,t1.eng_id,t1.work_type,t1.is_finish,t1.staff_id,
    t2.DESIGN_RESULT_ID,t2.SUBMIT_ID,t2.DEPT_TYPE
 from t_asse_design_work_todo t1
LEFT JOIN t_asse_design_result t2 
on  (
    CONVERT(t1.staff_id USING utf8)=CONVERT(t2.SUBMIT_ID USING utf8)
    and CONVERT(t1.eng_id USING utf8)=CONVERT(t2.ENG_ID USING utf8)
    )
where t1.is_finish='1' and  ISNULL(t2.SUBMIT_ID)