SQL server 2005新增的幾個函數,分別是row_number( )、rank( )、,DENSE_RANK( )、ntile( )下面以實例分別簡單講解。
1.row_number( )
先來點數據,先建個表
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')
直接用例子說明問題:
SELECT ROW_NUMBER() OVER (ORDER BY Age) AS [Row Number by Age],
FirstName,
Age
FROM Person
出現的數據如下
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
可以觀察到,是根據年齡升序排列了，并且row_number()是給出了序列號了,這個序列號被重命名為Row Number by Age,
與sql server2000對比:
如果在sql server2000中實現相對麻煩一些，我們可以利用IDENTITY()函數實現，但IDENTITY()函數只能用在sql server2000臨時表中，因此需要將數據檢索到臨時表里。
select identity(int,1,1) as [Row Number by Age],FirstName,Age into #A from Person order by Age
select * from #A
drop table #a
如果不想按年齡排序,可以這樣寫
SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 1)) AS [Row Number by Record Set], FirstName, Age FROM Person
另外一個例子
SELECT ROW_NUMBER() OVER (PARTITION BY Gender ORDER BY Age) AS [Partition by Gender], FirstName, Age, Gender FROM Person
這里是按性別劃分區間了，同一性別再按年齡來排序,輸出結果如下
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開始,序號又從1,2,3開始了
2.RANK( )函數
先看例子
SELECT RANK() OVER (ORDER BY Age) AS [Rank by Age], FirstName, Age FROM Person
輸出如下:
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,同年嶺的話,將有相同的順序,順序成1,2,2,4了。
與sql server2000對比:
出現了RANK()函數實在是方便,在sql server2000里實現排序并列的問題麻煩很多。
select [Rank by Age]=isnull((select count(*) from person where Age>A.Age),0)+1,FirstName,Age from Person A order by [Rank by Age]
SELECT RANK() OVER(PARTITION BY Gender ORDER BY Age) AS [Partition by Gender],
FirstName, Age, Gender FROM Person輸出為
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,按性別分組了,每個性別分組里,繼續是用了rank( )函數
3.DENSE_RANK( )函數
SELECT DENSE_RANK() OVER (ORDER BY Age) AS [Dense Rank by Age],
FirstName,
Age
FROM Person
輸出結果為:
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函數區別是,順序始終是連續的,Doris 和George同年,都是排第2位,但之后的mary不象rank函數那樣排第4,而是排第3位了
4.ntile( )函數
SELECT FirstName,
Age,
NTILE(3) OVER (ORDER BY Age) AS [Age Groups]
FROM Person
輸出結果：
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
這個函數按照ntile(n)中的N,把記錄強制分成多少段,11條記錄現在分成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。