mysql分组取最大(最小、最新、前N条)条记录

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:

namevalmemo
a2a2
a1a1
a3a3
b1b1
b3b3
b2b2
b4b4
b5b5

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:

namevalmemo
a3a3
b5b5

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 < a.val)

方法三:

select a.* from tb a,(select name,min(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 , min(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name

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

以上五种方法运行的结果均为如下所示:

namevalmemo
a1a1
b1b1

按name分组取第一次出现的行所在的数据 

sql如下:

select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name
//这个是sql server的
//mysql应该是
select a.* from tb a where val = (select val from tb where name = a.name limit 1) order by a.name

结果如下:

namevalmemo
a2a2
b1b1

—–下面的没有验证– 感觉是sql-server的写法,mysql的随机是rand(),前几条记录是limit N.

按name分组随机取一条数据

sql如下:

select a.* from tb a where val = (select top 1 val from tb where name = a.name order by newid()) order by a.name

结果如下:

namevalmemo
a1a1
b3b3

按name分组取最小的两个(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) 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:

namevalmemo
a1a1
a2a2
b1b1
b2b2

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:

namevalmemo
a3a3
a2a2
b5b5
b4b4