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：

<pre class="wp-block-preformatted">CREATE TABLE `tb` (
  `id` int(<strong>11</strong>) NOT NULL AUTO_INCREMENT,
  `name` varchar(<strong>10</strong>) CHARACTER SET latin1 DEFAULT NULL,
  `val` int(<strong>11</strong>) DEFAULT NULL,
  `memo` varchar(<strong>20</strong>) CHARACTER SET latin1 DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=<strong>9</strong> DEFAULT CHARSET=utf8

<pre class="wp-block-preformatted">insert into tb values('a',    <strong>2</strong>,   'a2');
insert into tb values('a',    <strong>1</strong>,   'a1');
insert into tb values('a',    <strong>3</strong>,   'a3');
insert into tb values('b',    <strong>1</strong>,   'b1');
insert into tb values('b',    <strong>3</strong>,   'b3');
insert into tb values('b',    <strong>2</strong>,   'b2');
insert into tb values('b',    <strong>4</strong>,   'b4');
insert into tb values('b',    <strong>5</strong>,   '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：

<pre class="wp-block-preformatted">select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name

方法二：

<pre class="wp-block-preformatted">select a.* from tb a where not exists(select <strong>1</strong> from tb where name = a.name and val > a.val)

方法三：

<pre class="wp-block-preformatted">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：

<pre class="wp-block-preformatted">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：

<pre class="wp-block-preformatted">select a.* from tb a where <strong>1</strong> > (select count(*) from tb where name = a.name and val > a.val ) order by a.name

方法六:

<pre class="wp-block-preformatted">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：

<pre class="wp-block-preformatted">select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name

方法二：

<pre class="wp-block-preformatted">select a.* from tb a where not exists(select <strong>1</strong> from tb where name = a.name and val < a.val)

方法三：

<pre class="wp-block-preformatted">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：

<pre class="wp-block-preformatted">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：

<pre class="wp-block-preformatted">select a.* from tb a where <strong>1</strong> > (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：

| name | val | memo | |------|-----|------| | a | 1 | a1 | | b | 1 | b1 |

按name分组取第一次出现的行所在的数据

sql如下：

<pre class="wp-block-preformatted">select a.* from tb a where val = (select top <strong>1</strong> 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 <strong>1</strong>) order by a.name

结果如下：

| name | val | memo | |------|-----|------| | a | 2 | a2 | | b | 1 | b1 |

—–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：

<pre class="wp-block-code">```
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：

<figure class="wp-block-table">| name | val | memo |
|------|-----|------|
| a | 1 | a1 |
| b | 3 | b3 |

</figure>## 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：

| 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 |