mysql where 中有max()

数据表tableA是这样的。
id  username mark dateT
1   user1    78    2006
2   user2    45    2006
3   user1    89    2007
4   user2    78    2009

SELECT * FROM tableA a WHERE a.mark >= (SELECT MAX(b.mark) FROM tableA b WHERE b.username=a.username )

id  username mark  dateT
3  user1   89  2007
4  user2   78  2009