SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for test
-- ----------------------------
DROP TABLE IF EXISTS `test`;
CREATE TABLE `test` (
  `_id` int(11) NOT NULL AUTO_INCREMENT,
  `classs` varchar(20) DEFAULT NULL,
  `cores` int(64) DEFAULT NULL,
  PRIMARY KEY (`_id`),
  KEY `NAME_UN` (`classs`(4))
) ENGINE=InnoDB AUTO_INCREMENT=1212122 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of test
-- ----------------------------
INSERT INTO `test` VALUES ('1', 'tt', '10');
INSERT INTO `test` VALUES ('11', 'tt', '12');
INSERT INTO `test` VALUES ('12', 'tt', '13');
INSERT INTO `test` VALUES ('111', 'w', '1');
INSERT INTO `test` VALUES ('133', 'tt', '14');
INSERT INTO `test` VALUES ('1212', 'w', '12');
INSERT INTO `test` VALUES ('12121', 'w', '121');
INSERT INTO `test` VALUES ('121212', 'w', '121');





select t2._id,t2.classs,t2.cores,count(*) from test t1 join test t2 on t1.classs=t2.classs
where t1.cores >= t2.cores
GROUP BY t2._id,t2.classs,t2.cores
HAVING count(t2._id) <= 2 （这里的数字‘2’是你想取值的数  比如排名前2）


t2._id   t2.classs t2.cores  count(*)
12      tt      13         2
133      tt      14         1
12121       w      121 2
121212       w      121 2
主键        班级     分数      排名