#查询姓张的每个学生的最低分大于60的学号和姓名

SELECT r.studentno,studentname
FROM result r
INNER JOIN student s
ON r.`studentno`=s.`studentno`
WHERE s.`studentname` LIKE '张%' 
GROUP BY r.`studentno`
HAVING MIN(r.`score`)>60;

#查询生日在’1988-1-1’后的学生的姓名和专业名称

SELECT studentname,m.`majorname`
FROM student s
INNER JOIN major m 
ON s.`majorid`=m.`majorid`;
WHERE DATEDIFF(borndate,'1988-1-1')>0;

#查询每个专业的男生人数和女生人数分别是多少

SELECT COUNT(*),sex,majorid
FROM student
GROUP BY sex,majorid;

或

SELECT (SELECT COUNT(*) FROM student WHERE sex='男' AND s.majorid=majorid ),
             (SELECT COUNT(*) FROM student WHERE sex='女' AND s.majorid=majorid),
             majorid
FROM student s
GROUP BY majorid;

#查询专业和张翠山一样的学生的最低分

SELECT MIN(score)
FROM result r
WHERE r.`studentno`IN
(SELECT studentno
    FROM student s
    WHERE s.`majorid` =(
        SELECT majorid
        FROM student
        WHERE studentname='张翠山'
        )
)

#查询大于60分的学生的姓名、密码、专业名

SELECT studentname,loginpwd,majorname
FROM student s
INNER JOIN major m
ON s.`majorid`=m.`majorid`
INNER JOIN result r
ON r.`studentno`=s.`studentno`
WHERE r.`score`>60;

#按邮箱位数分组，查询每组的学生个数

SELECT COUNT(*)
FROM student
GROUP BY LENGTH(email);

#查询学生名、专业名、分数

SELECT studentname,majorname,score
FROM student s
INNER JOIN major m
ON s.`majorid`=m.`majorid`
INNER JOIN result r
ON r.`studentno`=s.`studentno`;

#查询哪个专业没有学生，分别用左连接和右连接实现

SELECT majorname
FROM major m
LEFT OUTER JOIN student s
ON m.`majorid`=s.`majorid`
WHERE s.`majorid` IS NULL;  

#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;