MYSQL-多表联结查询

1、DDL

CREATE TABLE `result` (
  `rid` int(11) NOT NULL AUTO_INCREMENT COMMENT '成绩编号',
  `testName` varchar(255) DEFAULT NULL COMMENT '测试名称',
  `score` double(4,2) DEFAULT NULL COMMENT '成绩',
  `studentId` int(11) DEFAULT NULL COMMENT '学生id',
  PRIMARY KEY (`rid`),
  KEY `studentId` (`studentId`),
  CONSTRAINT `result_ibfk_1` FOREIGN KEY (`studentId`) REFERENCES `student` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8;

CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '学号',
  `createDate` datetime DEFAULT NULL,
  `userName` varchar(20) DEFAULT NULL,
  `pwd` varchar(36) DEFAULT NULL,
  `phone` varchar(11) DEFAULT NULL,
  `age` tinyint(3) unsigned DEFAULT NULL,
  `sex` char(2) DEFAULT '男',
  `introduce` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

2、DML

SELECT studentId '学号',userName '学生名称',
sum (score) '学生各科目总分',
count (score) '考试科目数量',
AVG (score) '各科目平均分',
from result inner join student on result.studentId=student.id
GROUP BY studentId,userName
HAVING avg (score)>60
ORDER BY AVG(score) desc
SELECT * from result inner join student on result.studentId=student.id