数据库两表连查，多组数据对比问题

现在有两张表，要查每个部门里个人薪资大于部门平均薪资的人的所有信息。

SELECT c.id,c.name,c.bum,d.age,c.time,c.se,d.xinz 
from t2 c
LEFT JOIN (
SELECT a.sid,a.xinz,a.sex,a.age 
from t1 a 
LEFT JOIN (SELECT sex,avg(xinz) as xinz  FROM t1 GROUP BY sex) b 
on a.xinz>b.xinz and a.sex=b.sex 
WHERE b.xinz!='Null') d
on c.id=d.sid
where d.xinz!="Null"