mysql分组取最大(最小、最新、前N条)条记录 |
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在数据库开发过程中,我们要为每种类型的数据取出前几条记录,或者是取最新、最小、最大等等,这个该如何实现呢,本文章向大家介绍如何实现mysql分组取最大(最小、最新、前N条)条记录。需要的可以参考一下。
先看一下本示例中需要使用到的数据 创建表并插入数据: CREATE TABLE `tb` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(10) CHARACTER SET latin1 DEFAULT NULL, `val` int(11) DEFAULT NULL, `memo` varchar(20) CHARACTER SET latin1 DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 insert into tb values('a', 2, 'a2'); insert into tb values('a', 1, 'a1'); insert into tb values('a', 3, 'a3'); insert into tb values('b', 1, 'b1'); insert into tb values('b', 3, 'b3'); insert into tb values('b', 2, 'b2'); insert into tb values('b', 4, 'b4'); insert into tb values('b', 5, 'b5');数据表如下: name val memo a 2 a2 a 1 a1 a 3 a3 b 1 b1 b 3 b3 b 2 b2 b 4 b4 b 5 b5按name分组取val最大的值所在行的数据 方法一: select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name方法二: select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val)方法三: select a.* from tb a,(select name,max(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name方法四: select a.* from tb a inner join (select name , max(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by方法五: select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name方法六: select * from (select * from tb ORDER BY val desc) temp GROUP BY name ORDER BY val desc;
以上六种方法运行的结果均为如下所示: name val memo a 3 a3 b 5 b5小编推荐使用第一、第三、第四钟方法,结果显示第1,3,4种方法效率相同,第2,5种方法效率差些。 按name分组取val最小的值所在行的数据方法一: select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name方法二: select a.* from tb a where not exists(select 1 from tb where name = a.name and val (select count(*) from tb where name = a.name and val (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.val第二种方法: select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val) order by a.name,a.val第三种方法: select a.* from tb a where exists (select count(*) from tb where name = a.name and val < a.val having Count(*) < 2) order by a.name结果如下: name val memo a 1 a1 a 2 a2 b 1 b1 b 2 b2按name分组取最大的两个(N个)val 第一种方法: select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.val第二种方法: select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val desc) order by a.name,a.val第三种方法: select a.* from tb a where exists (select count(*) from tb where name = a.name and val > a.val having Count(*) < 2) order by a.name结果如下: name val memo a 3 a3 a 2 a2 b 5 b5 b 4 b4
转:http://www.manongjc.com/article/1082.html 同样问题:http://www.cnblogs.com/fps2tao/p/9038268.html
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