MySQL8.0窗口函数入门实践及总结

前言

MySQL8.0之前，做数据排名统计等相当痛苦，因为没有像Oracle、SQL SERVER 、PostgreSQL等其他数据库那样的窗口函数。但随着MySQL8.0中新增了窗口函数之后，针对这类统计就再也不是事了，本文就以常用的排序实例介绍MySQL的窗口函数。

1、准备工作

创建表及测试数据

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mysql> use testdb; Database changed /* 创建表 */ mysql> create table tb_score(id int primary key auto_increment,stu_no varchar (10),course varchar (50),score decimal (4,1)， key idx_stuNo_course(stu_no,course)); Query OK, 0 rows affected (0.03 sec)   mysql> show tables; + ------------------+ | Tables_in_testdb | + ------------------+ | tb_score  | + ------------------+   /* 新增一批测试数据 */ mysql> insert into tb_score(stu_no,course,score) values ( '2020001' , 'mysql' ,90),( '2020001' , 'C++' ,85),( '2020003' , 'English' ,100),( '2020002' , 'mysql' ,50),( '2020002' , 'C++' ,70),( '2020002' , 'English' ,99); Query OK, 6 rows affected (0.00 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> insert into tb_score(stu_no,course,score) values ( '2020003' , 'mysql' ,78),( '2020003' , 'C++' ,81),( '2020003' , 'English' ,80),( '2020004' , 'mysql' ,80),( '2020004' , 'C++' ,60),( '2020004' , 'English' ,100); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> insert into tb_score(stu_no,course,score) values ( '2020005' , 'mysql' ,98),( '2020005' , 'C++' ,96),( '2020005' , 'English' ,70),( '2020006' , 'mysql' ,60),( '2020006' , 'C++' ,90),( '2020006' , 'English' ,70); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> insert into tb_score(stu_no,course,score) values ( '2020007' , 'mysql' ,50),( '2020007' , 'C++' ,66),( '2020007' , 'English' ,76),( '2020008' , 'mysql' ,90),( '2020008' , 'C++' ,69),( '2020008' , 'English' ,86); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> insert into tb_score(stu_no,course,score) values ( '2020009' , 'mysql' ,70),( '2020009' , 'C++' ,66),( '2020009' , 'English' ,86),( '2020010' , 'mysql' ,75),( '2020010' , 'C++' ,76),( '2020010' , 'English' ,81); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> insert into tb_score(stu_no,course,score) values ( '2020011' , 'mysql' ,90),( '2020012' , 'C++' ,85),( '2020011' , 'English' ,84),( '2020012' , 'English' ,75),( '2020013' , 'C++' ,96),( '2020013' , 'English' ,88); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0

2、统计每门课程分数的排名

根据每门课程的分数从高到低进行排名，此时，会出现分数相同时怎么处理的问题，下面就根据不同的窗口函数来处理不同场景的需求

ROW_NUMBER

由结果可以看出，分数相同时按照学号顺序进行排名

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mysql> select stu_no,course,score, row_number()over(partition by course order by score desc ) rn   -> from tb_score; + ---------+---------+-------+----+ | stu_no | course | score | rn | + ---------+---------+-------+----+ | 2020005 | C++ | 96.0 | 1 | | 2020013 | C++ | 96.0 | 2 | | 2020006 | C++ | 90.0 | 3 | | 2020001 | C++ | 85.0 | 4 | | 2020012 | C++ | 85.0 | 5 | | 2020003 | C++ | 81.0 | 6 | | 2020010 | C++ | 76.0 | 7 | | 2020002 | C++ | 70.0 | 8 | | 2020008 | C++ | 69.0 | 9 | | 2020007 | C++ | 66.0 | 10 | | 2020009 | C++ | 66.0 | 11 | | 2020004 | C++ | 60.0 | 12 | | 2020003 | English | 100.0 | 1 | | 2020004 | English | 100.0 | 2 | | 2020002 | English | 99.0 | 3 | | 2020013 | English | 88.0 | 4 | | 2020008 | English | 86.0 | 5 | | 2020009 | English | 86.0 | 6 | | 2020011 | English | 84.0 | 7 | | 2020010 | English | 81.0 | 8 | | 2020003 | English | 80.0 | 9 | | 2020007 | English | 76.0 | 10 | | 2020012 | English | 75.0 | 11 | | 2020005 | English | 70.0 | 12 | | 2020006 | English | 70.0 | 13 | | 2020005 | mysql | 98.0 | 1 | | 2020001 | mysql | 90.0 | 2 | | 2020008 | mysql | 90.0 | 3 | | 2020011 | mysql | 90.0 | 4 | | 2020004 | mysql | 80.0 | 5 | | 2020003 | mysql | 78.0 | 6 | | 2020010 | mysql | 75.0 | 7 | | 2020009 | mysql | 70.0 | 8 | | 2020006 | mysql | 60.0 | 9 | | 2020002 | mysql | 50.0 | 10 | | 2020007 | mysql | 50.0 | 11 | + ---------+---------+-------+----+ 36 rows in set (0.00 sec)mysql> select stu_no,course,score, row_number()over(partition by course order by score desc ) rn   -> from tb_score; + ---------+---------+-------+----+ | stu_no | course | score | rn | + ---------+---------+-------+----+ | 2020005 | C++ | 96.0 | 1 | | 2020013 | C++ | 96.0 | 2 | | 2020006 | C++ | 90.0 | 3 | | 2020001 | C++ | 85.0 | 4 | | 2020012 | C++ | 85.0 | 5 | | 2020003 | C++ | 81.0 | 6 | | 2020010 | C++ | 76.0 | 7 | | 2020002 | C++ | 70.0 | 8 | | 2020008 | C++ | 69.0 | 9 | | 2020007 | C++ | 66.0 | 10 | | 2020009 | C++ | 66.0 | 11 | | 2020004 | C++ | 60.0 | 12 | | 2020003 | English | 100.0 | 1 | | 2020004 | English | 100.0 | 2 | | 2020002 | English | 99.0 | 3 | | 2020013 | English | 88.0 | 4 | | 2020008 | English | 86.0 | 5 | | 2020009 | English | 86.0 | 6 | | 2020011 | English | 84.0 | 7 | | 2020010 | English | 81.0 | 8 | | 2020003 | English | 80.0 | 9 | | 2020007 | English | 76.0 | 10 | | 2020012 | English | 75.0 | 11 | | 2020005 | English | 70.0 | 12 | | 2020006 | English | 70.0 | 13 | | 2020005 | mysql | 98.0 | 1 | | 2020001 | mysql | 90.0 | 2 | | 2020008 | mysql | 90.0 | 3 | | 2020011 | mysql | 90.0 | 4 | | 2020004 | mysql | 80.0 | 5 | | 2020003 | mysql | 78.0 | 6 | | 2020010 | mysql | 75.0 | 7 | | 2020009 | mysql | 70.0 | 8 | | 2020006 | mysql | 60.0 | 9 | | 2020002 | mysql | 50.0 | 10 | | 2020007 | mysql | 50.0 | 11 | + ---------+---------+-------+----+ 36 rows in set (0.00 sec)

DENSE_RANK

为了让分数相同时排名也相同，则可以使用DENSE_RANK函数，结果如下：

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mysql> select stu_no,course,score, DENSE_RANK()over(partition by course order by score desc ) rn   -> from tb_score ; + ---------+---------+-------+----+ | stu_no | course | score | rn | + ---------+---------+-------+----+ | 2020005 | C++ | 96.0 | 1 | | 2020013 | C++ | 96.0 | 1 | | 2020006 | C++ | 90.0 | 2 | | 2020001 | C++ | 85.0 | 3 | | 2020012 | C++ | 85.0 | 3 | | 2020003 | C++ | 81.0 | 4 | | 2020010 | C++ | 76.0 | 5 | | 2020002 | C++ | 70.0 | 6 | | 2020008 | C++ | 69.0 | 7 | | 2020007 | C++ | 66.0 | 8 | | 2020009 | C++ | 66.0 | 8 | | 2020004 | C++ | 60.0 | 9 | | 2020003 | English | 100.0 | 1 | | 2020004 | English | 100.0 | 1 | | 2020002 | English | 99.0 | 2 | | 2020013 | English | 88.0 | 3 | | 2020008 | English | 86.0 | 4 | | 2020009 | English | 86.0 | 4 | | 2020011 | English | 84.0 | 5 | | 2020010 | English | 81.0 | 6 | | 2020003 | English | 80.0 | 7 | | 2020007 | English | 76.0 | 8 | | 2020012 | English | 75.0 | 9 | | 2020005 | English | 70.0 | 10 | | 2020006 | English | 70.0 | 10 | | 2020005 | mysql | 98.0 | 1 | | 2020001 | mysql | 90.0 | 2 | | 2020008 | mysql | 90.0 | 2 | | 2020011 | mysql | 90.0 | 2 | | 2020004 | mysql | 80.0 | 3 | | 2020003 | mysql | 78.0 | 4 | | 2020010 | mysql | 75.0 | 5 | | 2020009 | mysql | 70.0 | 6 | | 2020006 | mysql | 60.0 | 7 | | 2020002 | mysql | 50.0 | 8 | | 2020007 | mysql | 50.0 | 8 | + ---------+---------+-------+----+ 36 rows in set (0.00 sec)

RANK

DENSE_RANK的结果是分数相同时排名相同了，但是下一个名次是紧接着上一个名次的，如果2个并列的第1之后，下一个我想是第3名，则可以使用RANK函数实现

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mysql> select stu_no,course,score, rank()over(partition by course order by score desc ) rn   -> from tb_score; + ---------+---------+-------+----+ | stu_no | course | score | rn | + ---------+---------+-------+----+ | 2020005 | C++ | 96.0 | 1 | | 2020013 | C++ | 96.0 | 1 | | 2020006 | C++ | 90.0 | 3 | | 2020001 | C++ | 85.0 | 4 | | 2020012 | C++ | 85.0 | 4 | | 2020003 | C++ | 81.0 | 6 | | 2020010 | C++ | 76.0 | 7 | | 2020002 | C++ | 70.0 | 8 | | 2020008 | C++ | 69.0 | 9 | | 2020007 | C++ | 66.0 | 10 | | 2020009 | C++ | 66.0 | 10 | | 2020004 | C++ | 60.0 | 12 | | 2020003 | English | 100.0 | 1 | | 2020004 | English | 100.0 | 1 | | 2020002 | English | 99.0 | 3 | | 2020013 | English | 88.0 | 4 | | 2020008 | English | 86.0 | 5 | | 2020009 | English | 86.0 | 5 | | 2020011 | English | 84.0 | 7 | | 2020010 | English | 81.0 | 8 | | 2020003 | English | 80.0 | 9 | | 2020007 | English | 76.0 | 10 | | 2020012 | English | 75.0 | 11 | | 2020005 | English | 70.0 | 12 | | 2020006 | English | 70.0 | 12 | | 2020005 | mysql | 98.0 | 1 | | 2020001 | mysql | 90.0 | 2 | | 2020008 | mysql | 90.0 | 2 | | 2020011 | mysql | 90.0 | 2 | | 2020004 | mysql | 80.0 | 5 | | 2020003 | mysql | 78.0 | 6 | | 2020010 | mysql | 75.0 | 7 | | 2020009 | mysql | 70.0 | 8 | | 2020006 | mysql | 60.0 | 9 | | 2020002 | mysql | 50.0 | 10 | | 2020007 | mysql | 50.0 | 10 | + ---------+---------+-------+----+ 36 rows in set (0.01 sec)

这样就实现了各种排序需求。

NTILE

NTILE函数的作用是对每个分组排名后，再将对应分组分成N个小组，例如

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mysql> select stu_no,course,score, rank()over(partition by course order by score desc )rn,NTILE(2)over(partition by course order by score desc ) rn_group from tb_score; + ---------+---------+-------+----+----------+ | stu_no | course | score | rn | rn_group | + ---------+---------+-------+----+----------+ | 2020005 | C++ | 96.0 | 1 | 1 | | 2020013 | C++ | 96.0 | 1 | 1 | | 2020006 | C++ | 90.0 | 3 | 1 | | 2020001 | C++ | 85.0 | 4 | 1 | | 2020012 | C++ | 85.0 | 4 | 1 | | 2020003 | C++ | 81.0 | 6 | 1 | | 2020010 | C++ | 76.0 | 7 | 2 | | 2020002 | C++ | 70.0 | 8 | 2 | | 2020008 | C++ | 69.0 | 9 | 2 | | 2020007 | C++ | 66.0 | 10 | 2 | | 2020009 | C++ | 66.0 | 10 | 2 | | 2020004 | C++ | 60.0 | 12 | 2 | | 2020003 | English | 100.0 | 1 | 1 | | 2020004 | English | 100.0 | 1 | 1 | | 2020002 | English | 99.0 | 3 | 1 | | 2020013 | English | 88.0 | 4 | 1 | | 2020008 | English | 86.0 | 5 | 1 | | 2020009 | English | 86.0 | 5 | 1 | | 2020011 | English | 84.0 | 7 | 1 | | 2020010 | English | 81.0 | 8 | 2 | | 2020003 | English | 80.0 | 9 | 2 | | 2020007 | English | 76.0 | 10 | 2 | | 2020012 | English | 75.0 | 11 | 2 | | 2020005 | English | 70.0 | 12 | 2 | | 2020006 | English | 70.0 | 12 | 2 | | 2020005 | mysql | 98.0 | 1 | 1 | | 2020001 | mysql | 90.0 | 2 | 1 | | 2020008 | mysql | 90.0 | 2 | 1 | | 2020011 | mysql | 90.0 | 2 | 1 | | 2020004 | mysql | 80.0 | 5 | 1 | | 2020003 | mysql | 78.0 | 6 | 1 | | 2020010 | mysql | 75.0 | 7 | 2 | | 2020009 | mysql | 70.0 | 8 | 2 | | 2020006 | mysql | 60.0 | 9 | 2 | | 2020002 | mysql | 50.0 | 10 | 2 | | 2020007 | mysql | 50.0 | 10 | 2 | + ---------+---------+-------+----+----------+ 36 rows in set (0.01 sec)

3、窗口函数小结

MySQL中还有许多其他的窗口函数，本文列举一些，大家可以自行测试

 

类别	函数	说明
排序	ROW_NUMBER	为表中的每一行分配一个序号，可以指定分组（也可以不指定）及排序字段
	DENSE_RANK	根据排序字段为每个分组中的每一行分配一个序号。 排名值相同时，序号相同，序号中没有间隙（1,1,2,3这种）
	RANK	根据排序字段为每个分组中的每一行分配一个序号。 排名值相同时，序号相同，但序号中存在间隙（1,1,3,4这种）
	NTILE	根据排序字段为每个分组中根据指定字段的排序再分成对应的组
分布	PERCENT_RANK	计算各分组或结果集中行的百分数等级
	CUME_DIST	计算某个值在一组有序的数据中累计的分布
前后	LEAD	返回分组中当前行之后的第N行的值。如果不存在对应行，则返回NULL。比如N=1时，第一名对应的值是第二名的，最后一名结果是NULL
	LAG	返回分组中当前行之前的第N行的值。如果不存在对应行，则返回NULL。比如N=1时，第一名对应的值是是NUL，最后一名结果是倒数第2的值
首尾中	FIRST_VALUE	返回每个分组中第一名对应的字段（或表达式）的值，例如本文中可以是第一名的分数、学号等任意字段的值
	LAST_VALUE	返回每个分组中最后一名对应的字段（或表达式）的值，例如本文中可以是最后一名的分数、学号等任意字段的值
	NTH_VALUE	返回每个分组中排名第N的对应字段（或表达式）的值，但小于N的行对应的值是NULL

 

MySQL中主要的窗口函数先总结这么多，建议还是得动手实践一番。另外，MySQL5.7及之前版本的排序方式的实现很多人已总结，也建议实操一番。

总结

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原文链接：https://www.cnblogs.com/gjc592/p/13194119.html