sqlserver 2005新增函數學習(轉載)

?

原文：SQL 2005新增的幾個函數之學習

今天學習了sql server 2005新增的幾個函數,分別是row_number(),rank,DENSE_RANK,ntile,下面以例子
分別簡單講解之
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, ? 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
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

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

?

5?? top n

?

? declare @n int

set @n=10;

select top(@n) * from table1

轉載于:https://www.cnblogs.com/yanglin/archive/2007/12/21/1009528.html

總結

以上是生活随笔為你收集整理的SQL 2005新增的几个函数之学习的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。