mysql rank函数怎么用

Mysql 的rank 函数如何实现

表特征：

mysql>select * from test

+------+------+

| a| b|

+------+------+

|1 | 20 |

|1 | 21 |

|1 | 24 |

|2 | 20 |

|2 | 32 |

|2 | 14 |

+------+------+

6 rows in set (0.00 sec)

现在，我们以a分组，查询b列最大的2个值。 这条sql要怎么写了？

1.创建表

Create Table: CREATE TABLE `sam` (

`a` int(11) DEFAULT NULL,

`b` int(11) DEFAULT NULL

) ENGINE=MyISAM DEFAULT CHARSET=utf8

2.插入模拟数据

INSERT INTO `sam` VALUES (1,10),(1,15),(1,20),(1,25),(2,20),(2,22),(2,33),(2,45)

+------+------+

| a| b|

+------+------+

|1 | 10 |

|1 | 15 |

|1 | 20 |

|1 | 25 |

|2 | 20 |

|2 | 22 |

|2 | 33 |

|2 | 45 |

+------+------+

3.SQL实现

select a,b,rownum,rank from

(select ff.a,ff.b,@rownum:=@rownum+1 rownum,if(@pa=ff.a,@rank:=@rank+1,@rank:=1) as rank,@pa:=ff.a

FROM

(select a,b from sam group by a,b order by a asc,b desc) ff,(select @rank:=0,@rownum:=0,@pa=null) tt) result

having rank <=2

4.结果：

+------+------+--------+------+

| a| b| rownum | rank |

+------+------+--------+------+

|1 | 25 | 1 |1 |

|1 | 20 | 2 |2 |

|2 | 45 | 5 |1 |

|2 | 33 | 6 |2 |

+------+------+--------+------+

4 rows in set (0.00 sec)

Mysql

的rank

函数如何实现

表特征：

mysql>

select

*

from

test

+------+------+

|

a

|

b

|

+------+------+

|

1

|

20

|

|

1

|

21

|

|

1

|

24

|

|

2

|

20

|

|

2

|

32

|

|

2

|

14

|

+------+------+

6

rows

in

set

(0.00

sec)

现在，我们以a分组，查询b列最大的2个值。

这条sql要怎么写了？

1.创建表

Create

Table:

CREATE

TABLE

`sam`

(

`a`

int(11)

DEFAULT

NULL,

`b`

int(11)

DEFAULT

NULL

)

ENGINE=MyISAM

DEFAULT

CHARSET=utf8

2.插入模拟数据

INSERT

INTO

`sam`

VALUES

(1,10),(1,15),(1,20),(1,25),(2,20),(2,22),(2,33),(2,45)

+------+------+

|

a

|

b

|

+------+------+

|

1

|

10

|

|

1

|

15

|

|

1

|

20

|

|

1

|

25

|

|

2

|

20

|

|

2

|

22

|

|

2

|

33

|

|

2

|

45

|

+------+------+

3.SQL实现

select

a,b,rownum,rank

from

(select

ff.a,ff.b,@rownum:=@rownum+1

rownum,if(@pa=ff.a,@rank:=@rank+1,@rank:=1)

as

rank,@pa:=ff.a

FROM

(select

a,b

from

sam

group

by

a,b

order

by

a

asc,b

desc)

ff,(select

@rank:=0,@rownum:=0,@pa=null)

tt)

result

having

rank

<=2

4.结果：

+------+------+--------+------+

|

a

|

b

|

rownum

|

rank

|

+------+------+--------+------+

|

1

|

25

|

1

|

1

|

|

1

|

20

|

2

|

2

|

|

2

|

45

|

5

|

1

|

|

2

|

33

|

6

|

2

|

+------+------+--------+------+

4

rows

in

set

(0.00

sec)