MySQL8.0窗口函数实践及小结
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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
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
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：
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
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++ MySQL8.0窗口函数之排名函数（rankdense_rank）的使用