CREATE TABLE `wsz2` (
`id` int(11) NOT NULL,
`name` varchar(5) NOT NULL,
`time` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`,`time`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;#
# 导出表中的数据 `wsz2`
#INSERT INTO `wsz2` (`id`, `name`, `time`) VALUES (1, 'a', '2011-05-01 10:00:00'),
(2, 'a', '2011-05-02 10:00:00'),
(3, 'b', '2011-05-02 12:00:00'),
(4, 'b', '2011-05-03 12:00:00');
--------------
取出来的结果就是这二条
(2, 'a', '2011-05-02 10:00:00'),(4, 'b', '2011-05-03 12:00:00');
`id` int(11) NOT NULL,
`name` varchar(5) NOT NULL,
`time` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`,`time`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;#
# 导出表中的数据 `wsz2`
#INSERT INTO `wsz2` (`id`, `name`, `time`) VALUES (1, 'a', '2011-05-01 10:00:00'),
(2, 'a', '2011-05-02 10:00:00'),
(3, 'b', '2011-05-02 12:00:00'),
(4, 'b', '2011-05-03 12:00:00');
--------------
取出来的结果就是这二条
(2, 'a', '2011-05-02 10:00:00'),(4, 'b', '2011-05-03 12:00:00');
and a.`time`<`time`)
[征集]分组取最大N条记录方法征集,及散分....
mysql> select * from wsz2;
+----+------+---------------------+
| id | name | time |
+----+------+---------------------+
| 1 | a | 2011-05-01 10:00:00 |
| 2 | a | 2011-05-02 10:00:00 |
| 3 | b | 2011-05-02 12:00:00 |
| 4 | b | 2011-05-03 12:00:00 |
+----+------+---------------------+
4 rows in set (0.00 sec)mysql> select * from (select * from wsz2 order by time desc) t group by name;
+----+------+---------------------+
| id | name | time |
+----+------+---------------------+
| 2 | a | 2011-05-02 10:00:00 |
| 4 | b | 2011-05-03 12:00:00 |
+----+------+---------------------+
2 rows in set (0.00 sec)mysql>
wsz2.name=table.name and table.zone='xxx'---------------
我是这么加的:select wsz2.*,table.* from (select * from wsz2 order by time desc) t,table where wsz2.name=table.name and table.zone='xxx' group by wsz2.name;
建议你列出你的表结构,并提供测试数据以及基于这些测试数据的所对应正确结果。
参考一下这个贴子的提问方式http://topic.csdn.net/u/20091130/20/8343ee6a-417c-4c2d-9415-fa46604a00cf.html
1. 你的 create table xxx .. 语句
2. 你的 insert into xxx ... 语句
3. 结果是什么样,(并给以简单的算法描述)
4. 你用的数据库名称和版本(经常有人在MS SQL server版问 MySQL)
这样想帮你的人可以直接搭建和你相同的环境,并在给出方案前进行测试,避免文字描述理解上的误差。
from (select * from wsz2 order by time desc) t Inner Join
table on t.name=table.name
where table.zone='xxx'
group by t.name
`id` int(11) NOT NULL,
`name` varchar(5) NOT NULL,
`time` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`,`time`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;#
# 导出表中的数据 `wsz2`
#INSERT INTO `wsz2` (`id`, `name`, `time`) VALUES (1, 'a', '2011-05-01 10:00:00'),
(2, 'a', '2011-05-02 10:00:00'),
(3, 'b', '2011-05-02 12:00:00'),
(4, 'b', '2011-05-03 12:00:00');
(5, 'c', '2011-05-03 12:00:00');
CREATE TABLE `table` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(5) NOT NULL,
`zone` varchar(10) NOT NULL,
PRIMARY KEY (`id`),
KEY `name` (`name`,`zone`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;#
# 导出表中的数据 `table`
#INSERT INTO `table` (`id`, `name`, `zone`) VALUES (1, 'a', '音乐组'),
(2, 'b', '音乐组'),
(3, 'c', '数学组');
--------------------------------------------------
取出来wsz2表的最后一个时间的记录,并且table.zone=音乐组 的结果就是这二条.
二表关联条件是:wsz2.name=table.name(2, 'a', '2011-05-02 10:00:00'),(4, 'b', '2011-05-03 12:00:00');
SELECT max(w.id), w.name, max(w.time)
FROM wsz2 w, table t
WHERE w.name = t.name
AND t.zone = 'xxx'
GROUP BY w.name-- 假设id是自增字段,假设table表内name可能重复
SELECT max(w.id), w.name, max(w.time)
FROM wsz2 w
WHERE EXISTS (SELECT 1 FROM table t WHERE w.name = t.name AND t.zone = 'xxx')
GROUP BY w.name
一般,id就是自增字段。time晚的,id必然大,因此没必要自联,直接max即可。
me and `table`.zone='音乐组' order by wsz2.time desc) t group by name;
+----+------+---------------------+
| id | name | time |
+----+------+---------------------+
| 2 | a | 2011-05-02 10:00:00 |
| 4 | b | 2011-05-03 12:00:00 |
+----+------+---------------------+
2 rows in set (0.05 sec)mysql>
FROM wsz2 w, table t
WHERE w.name = t.name
AND t.zone = '音乐组'
GROUP BY w.name
直接这样就可以了吧