mysql返回最后一列数据

获取MySQL的表中每个userid最后一条记录的方法,并且针对userid不唯一的情况,需要的朋友可以参考下

表结构

CREATE TABLE `t1` ( 
    `userid` int(11) DEFAULT NULL, 
    `atime` datetime DEFAULT NULL, 
    KEY `idx_userid` (`userid`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8； 

表数据:

MySQL> select * from t1; 
+--------+---------------------+ 
| userid | atime | 
+--------+---------------------+ 
| 1 | 2013-08-12 11:05:25 | 
| 2 | 2013-08-12 11:05:29 | 
| 3 | 2013-08-12 11:05:32 | 
| 5 | 2013-08-12 11:05:34 | 
| 1 | 2013-08-12 11:05:40 | 
| 2 | 2013-08-12 11:05:43 | 
| 3 | 2013-08-12 11:05:48 | 
| 5 | 2013-08-12 11:06:03 | 
+--------+---------------------+ 
8 rows in set (0.00 sec) 

其中userid不唯一，要求取表中每个userid对应的时间离现在最近的一条记录.初看到一个这条件一般都会想到借用临时表及添加主建借助于join操作之类的.
给一个简方法：

MySQL> select userid,substring_index(group_concat(atime order by atime desc),",",1) as atime from t1 group by userid; 
+--------+---------------------+ 
| userid | atime | 
+--------+---------------------+ 
| 1 | 2013-08-12 11:05:40 | 
| 2 | 2013-08-12 11:05:43 | 
| 3 | 2013-08-12 11:05:48 | 
| 5 | 2013-08-12 11:06:03 | 
+--------+---------------------+ 
4 rows in set (0.03 sec)