求一条SQL语句

Question

---------------------------
| from | to | text | time |
---------------------------
| seg | me | ye! | 4 |
---------------------------
| seg | me | ye! | 3 |
---------------------------
| seg | yu | ye! | 2 |
---------------------------
| seg | yu | ye! | 1 |
---------------------------

大概是这个样子的一个表，我想知道能不能用一条语句提取出from=seg下所有不同的to字段值的time最新的一条数据，如果不能一句话的话写成几句也成0_0，比如上面应该获取到

---------------------------
| from | to | text | time |
---------------------------
| seg | me | ye! | 4 |
---------------------------
| seg | yu | ye! | 2 |
---------------------------

这两条数据。

Answer 1

使用group by 汇总即可

select t.* from t , (
      select c_from,c_to,max(c_time ) as c_time
      from t
      where 
      c_from = 'seg'
      group by c_from,c_to ) t1
where 
t.c_from = t1.c_from 
and t.c_to = t1.c_to
and t.c_time = t1.c_time

Answer 2

SELECT   a.*
  FROM   user_post a, (  SELECT   content, MAX (post_date) post_date
                           FROM   user_post
                          WHERE   user_name = 'withrock'
                       GROUP BY   content) b
 WHERE   a.content = b.content AND a.post_date = b.post_date

这张表的结构和你的不太一样，不过描述的问题是一样的.