试试这个查询
如果只想user1使用此查询：
select username, course_id, max(ldate) as date
from tbl
where username='user1'
group by course_id
| USERNAME | COURSE_ID | DATE |
-------------------------------------
| user1 | 22 | 2013-06-03 |
| user1 | 54 | 2013-06-03 |
select username, course_id, max(ldate) as date
from tbl
group by username, course_id
在此查询中，user2还将包含的数据
| USERNAME | COURSE_ID | DATE |
-------------------------------------
| user1 | 22 | 2013-06-03 |
| user1 | 54 | 2013-06-03 |
| user2 | 71 | 2013-06-04 |
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