mysql组内排序

mysql组内排序

1 创建表和数据

1.1 建库

CREATE DATABASE test;
use test;

1.2 建表

CREATE TABLE `test` (
  `class` varchar(10) DEFAULT NULL,
  `name` varchar(10) DEFAULT NULL,
  `score` bigint(20) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

1.3 添加数据

# 插入数据
INSERT INTO test VALUES('1','a',2);
INSERT INTO test VALUES('1','b',1);;
INSERT INTO test VALUES('1','c',4);
INSERT INTO test VALUES('1','d',5);
INSERT INTO test VALUES('1','e',7);
INSERT INTO test VALUES('1','f',8);
INSERT INTO test VALUES('2','g',9);
INSERT INTO test VALUES('2','h',0);
INSERT INTO test VALUES('2','i',21);
INSERT INTO test VALUES('2','j',3);
INSERT INTO test VALUES('2','k',4);
INSERT INTO test VALUES('2','1',56);
INSERT INTO test VALUES('3','m',67);
INSERT INTO test VALUES('3','n',89);
INSERT INTO test VALUES('3','o',12);
INSERT INTO test VALUES('3','p',22);
INSERT INTO test VALUES('3','q',23);
INSERT INTO test VALUES('3','r',42);
INSERT INTO test VALUES('3','s',26);

2 组内排序

SELECT a.*,count(1) as rank FROM `test` as a join test as b on a.class=b.class and a.score<=b.score GROUP BY a.class,a.name;


# 核心思想：做同组(同班)的笛卡尔积
# 和自己做连接(条件是班级相同，分数低于同班其他人)
# 然后按班级分组(为了聚合，使用count聚合函数),名字分组(重新打散分组)
# 获取的结果是名字，班级，分数，低于其他人的次数(即分数的名次)