mysql多表查询20题

+-------------------+
| Tables_in_dapeng3 |
+-------------------+
| class |
| course |
| s1 |
| score |
| student |
| teacher |
+-------------------+
6 rows in set (0.00 sec)

mysql> select * from class;
+----+--------------+
| id | caption |
+----+--------------+
| 1 | 三年二班 |
| 2 | 三年三班 |
| 3 | 一年二班 |
+----+--------------+
3 rows in set (0.11 sec)

mysql> select * from course;
+----+--------+------------+
| id | cname | teacher_id |
+----+--------+------------+
| 1 | 生物 | 1 |
| 2 | 物理 | 2 |
| 3 | 体育 | 3 |
| 4 | 美术 | 2 |
+----+--------+------------+
4 rows in set (0.00 sec)

mysql> select * from student;
+----+--------+--------+----------+
| id | sname | gender | class_id |
+----+--------+--------+----------+
| 1 | 铁蛋 | male | 2 |
| 2 | 钢蛋 | female | 1 |
| 3 | 铜蛋 | male | 3 |
| 4 | 银弹 | male | 1 |
| 5 | ety | male | 1 |
| 6 | yuu | female | 2 |
+----+--------+--------+----------+
6 rows in set (0.11 sec)

mysql> select * from teacher;
+----+-----------------+
| id | tname |
+----+-----------------+
| 1 | 张磊老师 |
| 2 | 李平老师 |
| 3 | 刘海燕老师 |
| 4 | 朱云海老师 |
| 5 | 李杰老师 |
+----+-----------------+
5 rows in set (0.11 sec)

mysql> select * from score;
+----+------------+-----------+--------+
| id | student_id | course_id | number |
+----+------------+-----------+--------+
| 1 | 1 | 1 | 100 |
| 2 | 2 | 1 | 58 |
| 3 | 2 | 2 | 56 |
| 4 | 3 | 3 | 90 |
+----+------------+-----------+--------+

1、查询所有的课程的名称以及对应的任课老师姓名
mysql> select course.cname,teacher.tname from course inner join teacher on course.teacher_id = teacher.id;
+--------+-----------------+
| cname  | tname           |
+--------+-----------------+
| 生物   | 张磊老师        |
| 物理   | 李平老师        |
| 美术   | 李平老师        |
| 体育   | 刘海燕老师      |
+--------+-----------------+

2、查询学生表中男女生各有多少人
mysql> select gender,count(gender) as male_count from student where gender = 'male' group by gender ;
+--------+------------+
| gender | male_count |
+--------+------------+
| male   |          4 |
+--------+------------+
1 row in set (0.00 sec)

mysql> select gender,count(gender) as male_count from student where gender = 'female' group by gender ;
+--------+------------+
| gender | male_count |
+--------+------------+
| female |          2 |
+--------+------------+

3、查询物理成绩等于100的学生的姓名
mysql> select sname from (select score.student_id,score.number,student.id,student.sname
 from score inner join student where student.id = score.student_id) as t1 where number = 100;
+--------+
| sname  |
+--------+
| 铁蛋   |
+--------+

4、查询成绩大于八十分的同学的姓名和平均成绩
mysql> select student.id,student.sname,score.student_id,score.number from student inner join 
score on student.id = score.student_id where score.number > 80 ;
+----+--------+------------+--------+
| id | sname  | student_id | number |
+----+--------+------------+--------+
|  3 | 铜蛋   |          3 |     90 |
|  1 | 铁蛋   |          1 |    100 |
|  4 | 银弹   |          4 |     98 |
+----+--------+------------+--------+

mysql> select avg(number) from (select student.id,student.sname,score.student_id,score.number
 from student inner join score on student.id = score.student_id where score.number > 80) as t;
+-------------+
| avg(number) |
+-------------+
|     96.0000 |
+-------------+

5、查询所有学生的学号，姓名,总成绩
mysql> select student.id,student.sname,t1.total_num from student left join(select score.student_id,
sum(score.number) as total_num from score group by score.student_id) as t1 on student.id = t1.student_id;
+----+--------+-----------+
| id | sname  | total_num |
+----+--------+-----------+
|  1 | 铁蛋   |       100 |
|  2 | 钢蛋   |        80 |
|  3 | 铜蛋   |        90 |
|  4 | 银弹   |        98 |
|  5 | ety    |      NULL |
|  6 | yuu    |      NULL |
+----+--------+-----------+

6、 查询姓李老师的个数
mysql> select tname from teacher where tname like '李%';
+--------------+
| tname        |
+--------------+
| 李平老师     |
| 李杰老师     |
+--------------+

7、 查询没有报李平老师课的学生姓名（未完成）
结果：学生姓名
查看李平老师教授的课程，然后和学生表建立关联
select student.sname,student.id from student left join
(select teacher.id,course.teacher_id,course.cname,teacher.tname from teacher
 left join course on teacher.id = course.teacher_id) as t1 ;

8、 查询物理课程比生物课程高的学生的学号
结果：学生的学号-student.id
score绑定课程
mysql> select t1.student_id from (select student_id,number from score
 where course_id = (select id from course where cname = '物理')) as t1 inner join
 (select student_id,number from score where course_id = (select id from course where cname = '生物'))
 as t2 on t1.student_id = t2.student_id where t1.number > t2.number;
+------------+
| student_id |
+------------+
|          2 |
+------------+
9、 查询没有同时选修物理课程和体育课程的学生姓名
结果：学生姓名
select student.sname from student where id in(select student_id from score where
course_id in(select id from course where cname = '物理' or cname = '体育')
group by student_id having count(course_id) = 1);

10、查询挂科超过两门(包括两门)的学生姓名和班级
结果：学生姓名和班级
mysql> select student.sname,class.caption from student inner join(select student_id from score where number <60
group by student_id having count(course_id) >= 2) as t1 inner join class on student.id = t1.student_id and
student.class_id = class.id;
流程注释：select 字段 from table. table里有学生姓名和班级，假设先把学生表和班级表连接起来，他们有共同字段class_id，内连接后可得到一张
学生对应班级的表。然后查询score表里的学生的每门成绩，如果有两门不到60的，获得该学生student_id，然后把上个表当作参数传入。
+--------+--------------+
| sname  | caption      |
+--------+--------------+
| 钢蛋   | 三年二班     |
+--------+--------------+

11 、查询选修了所有课程的学生姓名
mysql> select student.sname from student where id in (select student_id from score group by student_id having
count(course_id) = (select count(id) from course));
Empty set (0.14 sec)

12、查询李平老师教的课程的所有成绩记录
mysql> select * from score where course_id in (select id from course inner join
teacher on course.teacher_id = teacher.id where teacher.tname = '李平老师');

13、查询全部学生都选修了的课程号和课程名
mysql> select id,cname from course where id in (select course_id from score group by course_id
having count(student_id) = (select count(id) from student));
Empty set (0.01 sec)

14、查询每门课程被选修的次数
mysql> select course_id,count(student_id) from score group by course_id;
+-----------+-------------------+
| course_id | count(student_id) |
+-----------+-------------------+
|         1 |                 2 |
|         2 |                 1 |
|         3 |                 1 |
+-----------+-------------------+

15、查询只选修了一门课程的学生姓名和学号
mysql> select id,sname from student where id in (select student_id from score group by student_id having count(course_id) = 1);
+----+--------+
| id | sname  |
+----+--------+
|  1 | 铁蛋   |
|  3 | 铜蛋   |
+----+--------+

16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
mysql> select distinct number from score order by number desc;
+--------+
| number |
+--------+
|    100 |
|     90 |
|     58 |
|     56 |
+--------+

17、查询平均成绩大于85的学生姓名和平均成绩
mysql> select sname,t1.avg_num from student inner join (select student_id,avg(number) as avg_num from score group by student_id having avg(number) >85) as t1 on student.id = t1.student_id;
+--------+----------+
| sname  | avg_num  |
+--------+----------+
| 铁蛋   | 100.0000 |
| 铜蛋   |  90.0000 |
+--------+----------+
2 rows in set (0.11 sec)

18、查询生物成绩不及格的学生姓名和对应生物分数
SELECT
    sname ,
    number
FROM
    score
LEFT JOIN course ON score.course_id = course.id
LEFT JOIN student ON score.student_id = student.id
WHERE
    course.cname = '生物'
AND score.number < 60;
+--------+--------+
| sname  | number |
+--------+--------+
| 钢蛋   |     58 |
+--------+--------+

19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
SELECT
    sname
FROM
    student
WHERE
    id = (
        SELECT
            student_id
        FROM
            score
        WHERE
            course_id IN (
                SELECT
                    course.id
                FROM
                    course
                INNER JOIN teacher ON course.teacher_id = teacher.id
                WHERE
                    teacher.tname = '李平老师'
            )
        GROUP BY
            student_id
        ORDER BY
            AVG(number) DESC
        LIMIT 1
    );

+--------+
| sname  |
+--------+
| 钢蛋   |
+--------+

20、查询每门课程成绩最好的前两名学生姓名