mysql练习题99

 一、查询每个专业的学生人数
 SELECT COUNT(*)
 FROM student
 GROUP BY majorid;

 二、查询参加考试的学生中，每个学生的平均分、最高分
 SELECT avg(score),MAX(score),studentno
 FROM result
 GROUP BY stduentno;

 三、查询姓张的每个学生的最低分大于60的学号、姓名
 SELECT s.studentid,s.studentname,MIN(score)
 FROM student s
 JOIN result r
 on s.studentno=r.studentno
 where s.studentname LIKE '张%'
 GROUP BY studentno
 HAVING min(score)>60;

 四、查询专业生日在“1988-1-1”后的学生姓名、专业名称
 SELECT studentname,majorname,borndate
 FROM student s
 join major m
 on s.majorid=m.majorid
 where DATEDIFF(borndate,'1988-1-1')>0;

 #五、查询每个专业的男生人数和女生人数分别是多少
 #方式一：
 SELECT COUNT(*) 个数,majorid,sex
 FROM student
 GROUP BY sex,majorid;

 方式二：
 SELECT majorid,
 (SELECT COUNT(*) FROM student where sex='男' and majorid=s.majorid) 男,
 (SELECT COUNT(*) FROM student where sex='女' and majorid=s.majorid) 女
 FROM student s
 GROUP BY majorid 

 六、查询专业和张翠山一样的学生的最低分
 SELECT MIN(score)
 FROM result
 where studentno in (
 SELECT studentno
 FROM student
 WHERE mojorid=(SELECT majorid
 FROM student
 where studentname='张翠山'));

 七、查询大于60分的学生的姓名、密码、专业名
 SELECT studentname,loginpwd,majorname
 FROM student  s
 join result r
 on s.studentno=r.studentno
 JOIN major m
 on s.majorid=m.majorid
 where r.score>60;

 八、按邮箱位数分组，查询每组的学生个数
 SELECT COUNT(*)
 FROM student
 GROUP BY LENGTH(email);

 九、查询学生名、专业名、分数
 SELECT studentname,majorname,score
 FROM student s
 JOIN major m
 on s.majorid=m.majorid
 JOIN s.studentno=r.studentno;

 十、查询哪个专业没有学生，分别用左连接和右连接实现
 SELECT majorid,majorname
 from major m
 LEFT JOIN student s
 on m.majorid=s.majorid
 where s.studentno is null

 十一、查询没有成绩的学生人数
 SELECT COUNT(*)
 FROM student s
 LEFT JOIN result r on s.studentno=r.studentno
 where r.id is null