SQL连接并聚合多个表

select s.screenid, s.description
, CASE MAX(CASE rf.status WHEN 'E' THEN 2 WHEN 'V' THEN 1 ELSE 0 END)
    WHEN 2 THEN 'E'
    WHEN 1 THEN 'V'
    ELSE 'N' END as status
from user_roles ur
join role_functions rf on rf.roleid = ur.roleid
join function_screens fs on fs.functionid = rf.functionid
join screens s on s.screenid = fs.screenid
where ur.userid = :theuser
group by s.screenid, s.description
order by s.screenid