前言
MySQL8.0之前，做數(shù)據(jù)排名統(tǒng)計(jì)等相當(dāng)痛苦，因?yàn)闆]有像Oracle、SQL SERVER 、PostgreSQL等其他數(shù)據(jù)庫那樣的窗口函數(shù)。但隨著MySQL8.0中新增了窗口函數(shù)之后，針對這類統(tǒng)計(jì)就再也不是事了，本文就以常用的排序?qū)嵗榻BMySQL的窗口函數(shù)。
1、準(zhǔn)備工作
創(chuàng)建表及測試數(shù)據(jù)
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mysql> use testdb;Database changed/* 創(chuàng)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 |+------------------+/* 新增一批測試數(shù)據(jù) */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: 0mysql> 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: 0mysql> 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: 0mysql> 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: 0mysql> 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: 0mysql> 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、統(tǒng)計(jì)每門課程分?jǐn)?shù)的排名
根據(jù)每門課程的分?jǐn)?shù)從高到低進(jìn)行排名，此時(shí)，會出現(xiàn)分?jǐn)?shù)相同時(shí)怎么處理的問題，下面就根據(jù)不同的窗口函數(shù)來處理不同場景的需求
ROW_NUMBER
由結(jié)果可以看出，分?jǐn)?shù)相同時(shí)按照學(xué)號順序進(jìn)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
為了讓分?jǐn)?shù)相同時(shí)排名也相同，則可以使用DENSE_RANK函數(shù)，結(jié)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的結(jié)果是分?jǐn)?shù)相同時(shí)排名相同了，但是下一個(gè)名次是緊接著上一個(gè)名次的，如果2個(gè)并列的第1之后，下一個(gè)我想是第3名，則可以使用RANK函數(shù)實(shí)現(xiàn)
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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) |
這樣就實(shí)現(xiàn)了各種排序需求。
NTILE
NTILE函數(shù)的作用是對每個(gè)分組排名后，再將對應(yīng)分組分成N個(gè)小組，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、窗口函數(shù)小結(jié)
MySQL中還有許多其他的窗口函數(shù)，本文列舉一些，大家可以自行測試
| 類別 | 函數(shù) | 說明 |
| 排序 | ROW_NUMBER | 為表中的每一行分配一個(gè)序號，可以指定分組（也可以不指定）及排序字段 |
| DENSE_RANK | 根據(jù)排序字段為每個(gè)分組中的每一行分配一個(gè)序號。 排名值相同時(shí)，序號相同，序號中沒有間隙（1,1,2,3這種） | |
| RANK | 根據(jù)排序字段為每個(gè)分組中的每一行分配一個(gè)序號。 排名值相同時(shí)，序號相同，但序號中存在間隙（1,1,3,4這種） | |
| NTILE | 根據(jù)排序字段為每個(gè)分組中根據(jù)指定字段的排序再分成對應(yīng)的組 | |
| 分布 | PERCENT_RANK | 計(jì)算各分組或結(jié)果集中行的百分?jǐn)?shù)等級 |
| CUME_DIST | 計(jì)算某個(gè)值在一組有序的數(shù)據(jù)中累計(jì)的分布 | |
| 前后 | LEAD | 返回分組中當(dāng)前行之后的第N行的值。如果不存在對應(yīng)行，則返回NULL。比如N=1時(shí)，第一名對應(yīng)的值是第二名的，最后一名結(jié)果是NULL |
| LAG | 返回分組中當(dāng)前行之前的第N行的值。如果不存在對應(yīng)行，則返回NULL。比如N=1時(shí)，第一名對應(yīng)的值是是NUL，最后一名結(jié)果是倒數(shù)第2的值 | |
| 首尾中 | FIRST_VALUE | 返回每個(gè)分組中第一名對應(yīng)的字段（或表達(dá)式）的值，例如本文中可以是第一名的分?jǐn)?shù)、學(xué)號等任意字段的值 |
| LAST_VALUE | 返回每個(gè)分組中最后一名對應(yīng)的字段（或表達(dá)式）的值，例如本文中可以是最后一名的分?jǐn)?shù)、學(xué)號等任意字段的值 | |
| NTH_VALUE |
返回每個(gè)分組中排名第N的對應(yīng)字段（或表達(dá)式）的值，但小于N的行對應(yīng)的值是NULL |
MySQL中主要的窗口函數(shù)先總結(jié)這么多，建議還是得動手實(shí)踐一番。另外，MySQL5.7及之前版本的排序方式的實(shí)現(xiàn)很多人已總結(jié)，也建議實(shí)操一番。
總結(jié)
到此這篇關(guān)于MySQL8.0窗口函數(shù)入門實(shí)踐及總結(jié)的文章就介紹到這了,更多相關(guān)MySQL8.0窗口函數(shù)實(shí)踐內(nèi)容請搜索服務(wù)器之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持服務(wù)器之家！
原文鏈接：https://www.cnblogs.com/gjc592/p/13194119.html
