SQL Server-- Ranking functions
今天学习了sql server 2005新增的几个函数,分别是row_number(),rank,DENSE_RANK,ntile,下面以例子
分别简单讲解之
1.row_number
先来点数据,先建个表
分别简单讲解之
1.row_number
先来点数据,先建个表
SET NOCOUNT ON
CREATE TABLE Person(
FirstName VARCHAR(10),
Age INT,
Gender CHAR(1))
INSERT INTO Person VALUES ('Ted',23,'M')
INSERT INTO Person VALUES ('John',40,'M')
INSERT INTO Person VALUES ('George',6,'M')
INSERT INTO Person VALUES ('Mary',11,'F')
INSERT INTO Person VALUES ('Sam',17,'M')
INSERT INTO Person VALUES ('Doris',6,'F')
INSERT INTO Person VALUES ('Frank',38,'M')
INSERT INTO Person VALUES ('Larry',5,'M')
INSERT INTO Person VALUES ('Sue',29,'F')
INSERT INTO Person VALUES ('Sherry',11,'F')
INSERT INTO Person VALUES ('Marty',23,'F')
直接用例子说明问题
SELECT ROW_NUMBER() OVER (ORDER BY Age) AS [Row Number by Age],
FirstName,
Age
FROM Person
出现的数据如下
Row Number by Age FirstName Age
-------------------- ---------- -----------
1 Larry 5
2 Doris 6
3 George 6
4 Mary 11
5 Sherry 11
6 Sam 17
7 Ted 23
8 Marty 23
9 Sue 29
10 Frank 38
11 John 40
可以观察到,是根据年龄升序排列了，并且row_number()是给出了序列号了,这个序列号被重命名为Row Number by Age,
如果不想按年龄排序,可以这样写
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) AS [Row Number by Record Set],
FirstName,
Age
FROM Person
另外一个例子
SELECT ROW_NUMBER() OVER (PARTITION BY Gender ORDER BY Age) AS [Partition by Gender],
FirstName,
Age,
Gender
FROM Person
这里是按性别划分区间了，同一性别再按年龄来排序,输出结果如下
Partition by Gender FirstName Age Gender
-------------------- ---------- ----------- ------
1 Doris 6 F
2 Mary 11 F
3 Sherry 11 F
4 Sue 29 F
1 Larry 5 M
2 George 6 M
3 Sam 17 M
4 Ted 23 M
5 Marty 23 M
6 Frank 38 M
7 John 40 M
注意,姓名M开始,序号又从1,2,3开始了
2 RANK函数
先看例子
SELECT RANK() OVER (ORDER BY Age) AS [Rank by Age], FirstName, Age FROM Person
输出如下
Rank by Age FirstName Age -------------------- ---------- ----------- 1 Larry 5 2 Doris 6 2 George 6 4 Mary 11 4 Sherry 11 6 Sam 17 7 Ted 23 7 Marty 23 9 Sue 29 10 Frank 38 11 John 40
看到了么,同年岭的话,将有相同的顺序,顺序成1,2,2,4了FirstName, Age, Gender FROM Person输出为
SELECT RANK() OVER (PARTITION BY Gender ORDER BY Age) AS [Partition by Gender],
Partition by Gender FirstName Age Gender -------------------- ---------- ----------- ------ 1 Doris 6 F 2 Mary 11 F 2 Sherry 11 F 4 Sue 29 F 1 Larry 5 M 2 George 6 M 3 Sam 17 M 4 Ted 23 M 4 Marty 23 M 6 Frank 38 M 7 John 40 M
可以看到,按性别分组了,每个性别分组里,继续是用了rank函数
3 DENSE_RANK 函数
SELECT DENSE_RANK() OVER (ORDER BY Age) AS [Dense Rank by Age],
FirstName,
Age
FROM Person
输出结果为
Dense Rank by Age FirstName Age
-------------------- ---------- -----------
1 Larry 5
2 Doris 6
2 George 6
3 Mary 11
3 Sherry 11
4 Sam 17
5 Ted 23
5 Marty 23
6 Sue 29
7 Frank 38
8 John 40
看到了么,和rank函数区别是,顺序始终是连续的,Doris 和George同年,都是排第2位,但之后的mary不象rank函数那样排第4,而是排第3位了
4 ntile函数
SELECT FirstName, Age, NTILE(3) OVER (ORDER BY Age) AS [Age Groups] FROM Person
输出
FirstName Age Age Groups ---------- ----------- -------------------- Larry 5 1 Doris 6 1 George 6 1 Mary 11 1 Sherry 11 2 Sam 17 2 Ted 23 2 Marty 23 2 Sue 29 3 Frank 38 3 John 40 3
这个函数按照ntile(n)中的N,把记录强制分成多少段,11条记录现在分成3段了,lary到mary是第1
段,sherry到maty是第2段,sue到john是第3段了