mysql--学生课程成绩表

创建表student:

CREATE TABLE `student` (
	`sid` INT(11) NOT NULL AUTO_INCREMENT,
	`sname` VARCHAR(20) NOT NULL DEFAULT '0',
	`sage` INT(11) NOT NULL DEFAULT '0',
	`sex` VARCHAR(10) NOT NULL DEFAULT '0',
　　　　 `sdept` VARCHAR(20) NULL DEFAULT NULL,
        PRIMARY KEY (`sid`) 
)

COLLATE='utf8_general_ci' 
ENGINE=InnoDB

创建表course:　

CREATE TABLE `course` (
	`cid` INT(11) NOT NULL AUTO_INCREMENT,
	`cname` VARCHAR(20) NOT NULL DEFAULT '0',
	`ccredit` INT(11) NOT NULL DEFAULT '0',
	`semester` INT(11) NOT NULL DEFAULT '0',
	`period` INT(11) NOT NULL DEFAULT '0',
	PRIMARY KEY (`cid`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
AUTO_INCREMENT=3;

创建表sc:

CREATE TABLE `sc` (
	`sid` INT(11) NOT NULL DEFAULT '0',
	`cid` INT(11) NOT NULL DEFAULT '0',
	`score` INT(11) NULL DEFAULT NULL,
	PRIMARY KEY (`sid`, `cid`),
	CONSTRAINT `FK_sc_course` FOREIGN KEY (`cid`) REFERENCES `course` (`cid`),
	CONSTRAINT `FK_sc_student` FOREIGN KEY (`sid`) REFERENCES `student` (`sid`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

查询:

1. 计算机系人名字和年龄:

select sname, sage from student where sdept="computer"

2. 数学成绩在80到100之间的名字和学科和分数:

select sname,cname,score from student s, course c, sc where s.sid=sc.sid and c.cid=sc.cid and sc.score between 80 and 100 and cname="数学"

3. 每个系多少学生:

select count(sdept),sdept from student group by sdept

4. 课程1比课程2分数高的学号:

select a.sid  from(select sid, score from sc where cid=1)a, (select sid,score from sc where cid=2)b
where a.score>b.score and a.sid=b.sid

5. 平均分大于80分的学号和平均分:

select sid, avg(score) from sc group by sid having avg(score)>70

6. 所有学生的学号, 姓名, 选课数, 总成绩:

select student.sid, sname, count(sc.cid),sum(sc.score) from student left outer join sc on student.sid=sc.sid group by student.sid;