MySQL实现分组取组内特定数据的功能

需求：在MySQL5.7环境下，查询下面表中，各个学科前两名的学生的成绩；

1.准备数据

窗机表以及向表中插入数据

创建一张表：

DROP TABLE IF EXISTS `grade`;
CREATE TABLE `grade` (
  `id` int(11) DEFAULT NULL,
  `kemu` varchar(255) DEFAULT NULL,
  `score` int(255) DEFAULT NULL,
  `no` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

　向表中插入数据：

INSERT INTO `grade` VALUES ('', '语文', '', '');
INSERT INTO `grade` VALUES ('', '数学', '', '');
INSERT INTO `grade` VALUES ('', '英语', '', '');
INSERT INTO `grade` VALUES ('', '语文', '', '');
INSERT INTO `grade` VALUES ('', '数学', '', '');
INSERT INTO `grade` VALUES ('', '数学', '', '');
INSERT INTO `grade` VALUES ('', '语文', '', '');
INSERT INTO `grade` VALUES ('', '英语', '', '');
INSERT INTO `grade` VALUES ('', '英语', '', '');
INSERT INTO `grade` VALUES ('', '数学', '', '');

2.MySQL编写语句

SELECT * from (
SELECT g.id,g.kemu,g.score,count(*) as rank  from grade g
LEFT JOIN grade g1
on g.kemu=g1.kemu
and g.score<=g1.score
GROUP BY g.id,g.kemu,g.score
ORDER BY g.id,g.kemu,g.score desc
) n where rank<=2 ORDER BY kemu,rank

通过函数方式实现可以参考下面的链接：

https://www.jianshu.com/p/32e8c40372b3

http://blog.51cto.com/mydbs/2159794?source=dra