SQL Server 2005新增函數簡介

            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，並且row_number()是給出了序列號了,這個序列號被重命名爲Row Number by Age,

與對比:
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裏。
 

如果不想按年齡排序,可以這樣寫
SELECT  (ORDER BY (SELECT 1)) AS [Row Number by Record Set],
FirstName,
Age
FROM Person

另外一個例子
SELECT  (PARTITION BY Gender ORDER BY Age) AS [Partition by Gender],
FirstName,
Age,
Gender
FROM Person

這裏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函數
        先看例子
SELECT  (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

看到了麼,同年嶺的話,將有相同的順序,順序成1,2,2,4了。

與對比:
出現了RANK()函數實在是方便,在sql server2000裏實現排序並列的問題麻煩很多。

SELECT (PARTITION BY Gender ORDER BY Age) AS [Partition by Gender],
FirstName, Age, Gender FROM Person輸出爲

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,每個性別分組裏,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

輸出結果爲:
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

看到了麼,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,但之後的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。