Sort out the four commonly used sorting functions in SQL

Catalog

Preface

1.ROW_NUMBER()

1.1 Examples of sorting student grades

2.RANK() 

3.DENSE_RANK() 

4.NTILE()

Preface

Today I will introduce four sorting functions that you don't often use , They are SQL Server Often used in sorting ROW_NUMBER(),RANK(),DENSE_RANK(),NTILE() These four good brothers .

We're writing SQL Code , As long as there is sorting , The first thing I think about is ORDER BY, So many friends think how easy it is to sort .

Today I will introduce four sorting functions that you don't often use , They are SQL Server Often used in sorting ROW_NUMBER(),RANK(),DENSE_RANK(),NTILE() These four good brothers .

Let's create a test data table first Scores：

WITH t AS(SELECT 1 StuID,70 ScoreUNION ALLSELECT 2,85UNION ALLSELECT 3,85UNION ALLSELECT 4,80UNION ALLSELECT 5,74)SELECT * INTO Scores FROM t;SELECT * FROM Scores

give the result as follows ：

1.ROW_NUMBER()

Definition ：ROW_NUMBER() The function is to make SELECT Sort the query data , Add a serial number to each piece of data , He can't be used to rank students' grades , Generally used for paging query , For example, before querying 10 individual Inquire about 10-100 A student . 

1.1 Examples of sorting student grades SELECTROW_NUMBER() OVER (ORDER BY SCORE DESC) AS [RANK],*FROM Scores;

give the result as follows ：

here RANK It's the order after each student's ranking , according to Score Conduct DESC In reverse order  

1.2 For the first 2 Score information of name  

SELECT * FROM (SELECT ROW_NUMBER() OVER (ORDER BY SCORE DESC) AS [RANK],*FROM Scores) t WHERE t.RANK=2;

result ：

The idea used here is The idea of paging query In the original sql Put another layer on the outside SELECTWHERE t.RANK>=1 AND t.RANK<=3 Is it to get the score information of the top three students .

2.RANK() 

Definition ：RANK() function , As the name suggests, the ranking function , You can rank a field , Here and ROW_NUMBER() What's different ？ROW_NUMBER() It's sort , When there are students with the same grades ,ROW_NUMBER() They sort them in turn , They have different serial numbers , and Rank() Is not the same . If the same , Their rankings are the same . Let's take an example :

Example ：

SELECT ROW_NUMBER() OVER (ORDER BY SCORE DESC) AS [RANK],*FROM Scores;SELECT RANK() OVER (ORDER BY SCORE DESC) AS [RANK],*FROM Scores;

result ：

It's on it ROW_NUMBER() The result of the function , Here is RANK() The result of the function .

When two students have the same grade, there is a change in it .RANK() yes 1-1-3-4-5, and ROW_NUMBER() Or 1-2-3-4-5, This is it. RANK() and ROW_NUMBER() The difference between the

3.DENSE_RANK() 

Definition ：DENSE_RANK() Function is also a ranking function , and RANK() Functions are similar , It's also about ranking fields , Then it and RANK() What's the difference ？ Especially for those who have the same achievements ,DENSE_RANK() The ranking is continuous ,RANK() It's the jump ranking , Generally, the ranking function used is RANK() Let's look at an example

Example ：

SELECTRANK() OVER (ORDER BY SCORE DESC) AS [RANK],*FROM Scores;SELECTDENSE_RANK() OVER (ORDER BY SCORE DESC) AS [RANK],*FROM Scores;

result ：

It's on it RANK() Result , Here is DENSE_RANK() Result .

4.NTILE()

Definition ：NTILE() The function distributes rows in an ordered partition to a specified number of groups , Each group has a number , Number from 1 Start , Like we said ' Partition ' equally , It's divided into several zones , How many in a district .  

SELECT NTILE(1) OVER (ORDER BY SCORE DESC) AS [RANK],* FROM Scores;SELECT NTILE(2) OVER (ORDER BY SCORE DESC) AS [RANK],* FROM Scores;SELECT NTILE(3) OVER (ORDER BY SCORE DESC) AS [RANK],* FROM Scores;

result ：

Is to query the records according to NTILE The parameters in the function are divided equally .

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