MySQL实现row_number分组排序

在主流的数据库中, 一般都是有row_number函数直接支持分组排序的, 但是MySQL没有.
但我们可以通过以下方式实现:

准备工作

1. 安装MySQL

brew install mysql
mysql.server start 

笔主MySQL版本

mysql  Ver 8.0.13 for osx10.14 on x86_64 (Homebrew)

若遇到问题, 请点击打开: MySQL ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO) 和客户端不能链接

创建row_number_test测试表

DROP TABLE IF EXISTS row_number_test;  
CREATE TABLE row_number_test(empid INT, deptid INT, salary DECIMAL(10, 2)); 
INSERT INTO row_number_test VALUES   
    (1,10,5500.00), 
    (2,10,4500.00), 
    (3,20,1900.00), 
    (4,20,4800.00), 
    (5,40,6500.00), 
    (6,40,14500.00), 
    (7,40,44500.00), 
    (8,50,6500.00), 
    (9,50,7500.00); 

实现代码如下

SELECT 
    empid, deptid, salary, rk 
FROM ( 
    SELECT 
        tmp.empid, tmp.deptid, tmp.salary, @rownum:=@rownum+1, 
        IF(@pdept=tmp.deptid, @rank:=@rank+1, @rank:=1) AS rk, 
        @pdept:=tmp.deptid
    FROM (
        SELECT empid, deptid, salary FROM row_number_test 
        ORDER BY deptid ASC, salary DESC
    ) tmp, (SELECT @rownum:=0, @pdept:=null, @rank:=0) a
) result; 

结果

+-------+--------+----------+------+
| empid | deptid | salary   | rk   |
+-------+--------+----------+------+
|     1 |     10 |  5500.00 |    1 |
|     2 |     10 |  4500.00 |    2 |
|     4 |     20 |  4800.00 |    1 |
|     3 |     20 |  1900.00 |    2 |
|     7 |     40 | 44500.00 |    1 |
|     6 |     40 | 14500.00 |    2 |
|     5 |     40 |  6500.00 |    3 |
|     9 |     50 |  7500.00 |    1 |
|     8 |     50 |  6500.00 |    2 |
+-------+--------+----------+------+
9 rows in set, 7 warnings (0.01 sec)

如有问题, 欢迎评论留言!