MySQL 经典练习 50 题（完美解答版）

一、创建数据库和表

        数据库
                学生表 student
                课程表 course
                教师表 teacher
                成绩表 score

        表关系

        创建数据库和表

        创建数据库

drop database if exists Mysql_test cascade;create database mysql_test;use mysql_test;

        创建学生表 student

create table student (    s_id int,    s_name varchar(8),    s_birth date,    s_sex varchar(4));

        插入学生数据

insert into student values(1,'赵雷','1990-01-01','男'),(2,'钱电','1990-12-21','男'),(3,'孙风','1990-05-20','男'),(4,'李云','1990-08-06','男'),(5,'周梅','1991-12-01','女'),(6,'吴兰','1992-03-01','女'),(7,'郑竹','1989-07-01','女'),(8,'王菊','1990-01-20','女');

        创建课程表 course

create table course (    c_id int,    c_name varchar(8),    t_id int);

        插入课程数据

insert into course values(1,'语文',2),(2,'数学',1),(3,'英语',3);

        创建教师表 teacher

create table teacher (    t_id int,    t_name varchar(8));

        插入教师数据

insert into teacher values(1,'张三'),(2,'李四'),(3,'王五');

        创建成绩表 score

create table score (    s_id int,    c_id int,    s_score int);

        插入成绩数据

insert into score values(1,1,80),(1,2,90),(1,3,99),(2,1,70),(2,2,60),(2,3,65),(3,1,80),(3,2,80),(3,3,80),(4,1,50),(4,2,30),(4,3,40),(5,1,76),(5,2,87),(6,1,31),(6,3,34),(7,2,89),(7,3,98);

二、经典练习 50 题
 

1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数

select s.*,sc1.s_score as score_01,sc2.s_score as score_02from student sinner join (    select * from score where c_id = 1) sc1on s.s_id = sc1.s_idinner join (    select * from score where c_id = 2) sc2on s.s_id = sc2.s_idwhere sc1.s_score > sc2.s_score;

+------+--------+------------+-------+----------+----------+
| s_id | s_name | s_birth    | s_sex | score_01 | score_02 |
+------+--------+------------+-------+----------+----------+
|    2 | 钱电   | 1990-12-21 | 男    |       70 |       60 |
|    4 | 李云   | 1990-08-06 | 男    |       50 |       30 |
+------+--------+------------+-------+----------+----------+

2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
 

select s.*,sc1.s_score as score_01,sc2.s_score as score_02from student sinner join (    select * from score where c_id = 1) sc1on s.s_id = sc1.s_idinner join (    select * from score where c_id = 2) sc2on s.s_id = sc2.s_idwhere sc1.s_score < sc2.s_score;

+------+--------+------------+-------+----------+----------+
| s_id | s_name | s_birth    | s_sex | score_01 | score_02 |
+------+--------+------------+-------+----------+----------+
|    1 | 赵雷   | 1990-01-01 | 男    |       80 |       90 |
|    5 | 周梅   | 1991-12-01 | 女    |       76 |       87 |
+------+--------+------------+-------+----------+----------+

3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩

select s.s_id,s.s_name,round(avg_score, 2) as avg_scorefrom student sinner join (    select s_id,avg(s_score) as avg_score    from score    group by s_id    having avg_score >= 60) t1on s.s_id = t1.s_id;

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    1 | 赵雷   | 89.67     |
|    2 | 钱电   | 65.00     |
|    3 | 孙风   | 80.00     |
|    5 | 周梅   | 81.50     |
|    7 | 郑竹   | 93.50     |
+------+--------+-----------+

4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩(包括有成绩的和无成绩的)

select s.s_id,s.s_name,ifnull(round(avg_score, 2), 0) as avg_scorefrom student sleft join (    select s_id,avg(s_score) as avg_score    from score    group by s_id) t1on s.s_id = t1.s_idwhere avg_score is null or avg_score < 60;

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    4 | 李云   | 40.00     |
|    6 | 吴兰   | 32.50     |
|    8 | 王菊   | 0.00      |
+------+--------+-----------+

5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩

select s.s_id,s.s_name,ifnull(cnt_course, 0) as cnt_course,ifnull(sum_score, 0) as sum_scorefrom student sleft join (    select s_id,count(*) as cnt_course,sum(s_score) as sum_score    from score    group by s_id) t1on s.s_id = t1.s_id;

+------+--------+------------+-----------+
| s_id | s_name | cnt_course | sum_score |
+------+--------+------------+-----------+
|    1 | 赵雷   |          3 | 269       |
|    2 | 钱电   |          3 | 195       |
|    3 | 孙风   |          3 | 240       |
|    4 | 李云   |          3 | 120       |
|    5 | 周梅   |          2 | 163       |
|    6 | 吴兰   |          2 | 65        |
|    7 | 郑竹   |          2 | 187       |
|    8 | 王菊   |          0 | 0         |
+------+--------+------------+-----------+

6、查询"李"姓老师的数量

select count(*) as cnt_name_lifrom teacherwhere t_name like '李%';

+-------------+
| cnt_name_li |
+-------------+
|           1 |
+-------------+

7、询学过"张三"老师授课的同学的信息

select s.*from student swhere s_id in (    select distinct s_id    from score sc    inner join (        select c_id        from course c        inner join teacher t on c.t_id = t.t_id        where t_name = '张三'    ) t1    on sc.c_id = t1.c_id);

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 赵雷   | 1990-01-01 | 男    |
|    2 | 钱电   | 1990-12-21 | 男    |
|    3 | 孙风   | 1990-05-20 | 男    |
|    4 | 李云   | 1990-08-06 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
|    7 | 郑竹   | 1989-07-01 | 女    |
+------+--------+------------+-------+

8、查询没学过"张三"老师授课的同学的信息

select s.*from student swhere s_id not in (    select distinct s_id    from score sc    inner join (        select c_id        from course c        inner join teacher t on c.t_id = t.t_id        where t_name = '张三'    ) t1    on sc.c_id = t1.c_id);

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    6 | 吴兰   | 1992-03-01 | 女    |
|    8 | 王菊   | 1990-01-20 | 女    |
+------+--------+------------+-------+

9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息

select s.*from student swhere s_id in (    select s_id    from score    where c_id in (1,2)    group by s_id    having count(*) = 2);

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 赵雷   | 1990-01-01 | 男    |
|    2 | 钱电   | 1990-12-21 | 男    |
|    3 | 孙风   | 1990-05-20 | 男    |
|    4 | 李云   | 1990-08-06 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
+------+--------+------------+-------+

10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息

select s.*from student swhere s_id in (    select s_id    from score    where c_id = 1    and s_id not in (        select s_id from score where c_id = 2    ));

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    6 | 吴兰   | 1992-03-01 | 女    |
+------+--------+------------+-------+

11、查询没有学全所有课程的同学的信息

select *from studentwhere s_id not in (    select s_id    from score    group by s_id    having count(*) = (        select count(*) from course    ));

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    5 | 周梅   | 1991-12-01 | 女    |
|    6 | 吴兰   | 1992-03-01 | 女    |
|    7 | 郑竹   | 1989-07-01 | 女    |
|    8 | 王菊   | 1990-01-20 | 女    |
+------+--------+------------+-------+

12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息

select *from studentwhere s_id in (    select distinct s_id    from score s    inner join (        select c_id from score where s_id = 1    ) t1    on s.c_id = t1.c_id);

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 赵雷   | 1990-01-01 | 男    |
|    2 | 钱电   | 1990-12-21 | 男    |
|    3 | 孙风   | 1990-05-20 | 男    |
|    4 | 李云   | 1990-08-06 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
|    6 | 吴兰   | 1992-03-01 | 女    |
|    7 | 郑竹   | 1989-07-01 | 女    |
+------+--------+------------+-------+

 

13、查询和"01"号的同学学习的课程完全相同的其他同学的信息

select *from studentwhere s_id in (     select s_id     from score s     inner join (        select c_id from score where s_id = 1     ) t1     on s.c_id = t1.c_id     where s_id != 1     group by s_id having count(*) = (        select count(*) from score where s_id = 1     ));

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    2 | 钱电   | 1990-12-21 | 男    |
|    3 | 孙风   | 1990-05-20 | 男    |
|    4 | 李云   | 1990-08-06 | 男    |
+------+--------+------------+-------+

查询没学过"张三"老师讲授的任一门课程的学生姓名

select s_namefrom studentwhere s_id not in (    select s_id    from score sc    inner join (        select c_id        from course c        inner join teacher t on c.t_id = t.t_id        where t_name = '张三'    ) t1    on sc.c_id = t1.c_id);

+--------+
| s_name |
+--------+
| 吴兰   |
| 王菊   |
+--------+

15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

select s.s_id,s.s_name,round(avg(s_score), 2) as avg_scorefrom student sinner join (    select s_id    from score    where s_score < 60    group by s_id    having count(*) >= 2) t1on s.s_id = t1.s_idinner join score sc on s.s_id = sc.s_idgroup by s.s_id;

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    4 | 李云   | 40.00     |
|    6 | 吴兰   | 32.50     |
+------+--------+-----------+

检索"01"课程分数小于60，按分数降序排列的学生信息

select s.*,s_score as score_01from student sinner join (    select s_id,s_score    from score    where c_id = 1    and s_score < 60) t1on s.s_id = t1.s_idorder by score_01 desc;

+------+--------+------------+-------+----------+
| s_id | s_name | s_birth    | s_sex | score_01 |
+------+--------+------------+-------+----------+
|    4 | 李云   | 1990-08-06 | 男    |       50 |
|    6 | 吴兰   | 1992-03-01 | 女    |       31 |
+------+--------+------------+-------+----------+

17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

select    s.s_id as 学号,s.s_name as 姓名,    sum(case c_id when 1 then s_score else 0 end) as 语文,    sum(case c_id when 2 then s_score else 0 end) as 数学,    sum(case c_id when 3 then s_score else 0 end) as 英语,    ifnull(round(avg(s_score), 2), 0) as 平均成绩from student sleft join score sc on s.s_id = sc.s_idgroup by s.s_idorder by 平均成绩 desc;

+------+------+------+------+------+----------+
| 学号 | 姓名 | 语文 | 数学 | 英语 | 平均成绩 |
+------+------+------+------+------+----------+
|    7 | 郑竹 | 0    | 89   | 98   | 93.50    |
|    1 | 赵雷 | 80   | 90   | 99   | 89.67    |
|    5 | 周梅 | 76   | 87   | 0    | 81.50    |
|    3 | 孙风 | 80   | 80   | 80   | 80.00    |
|    2 | 钱电 | 70   | 60   | 65   | 65.00    |
|    4 | 李云 | 50   | 30   | 40   | 40.00    |
|    6 | 吴兰 | 31   | 0    | 34   | 32.50    |
|    8 | 王菊 | 0    | 0    | 0    | 0.00     |
+------+------+------+------+------+----------+

18、查询各科成绩最高分、最低分和平均分，以如下形式显示：
课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率
– 及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90

select    c.c_id as 课程ID,c.c_name as 课程name,    max(s_score) as 最高分,    min(s_score) as 最低分,    round(avg(s_score), 2) as 平均分,    concat(round(sum(case when s_score >= 60 then 1 else 0 end) / count(*) * 100, 2), '%') as 及格率,    concat(round(sum(case when s_score between 70 and 80 then 1 else 0 end) / count(*) * 100, 2), '%') as 中等率,    concat(round(sum(case when s_score between 80 and 90 then 1 else 0 end) / count(*) * 100, 2), '%') as 优良率,    concat(round(sum(case when s_score >= 90 then 1 else 0 end) / count(*) * 100, 2), '%') as 优秀率from course cinner join score s on c.c_id = s.c_idgroup by c.c_id;

+--------+----------+--------+--------+--------+--------+--------+--------+--------+
| 课程ID | 课程name | 最高分 | 最低分 | 平均分 | 及格率 | 中等率 | 优良率 | 优秀率 |
+--------+----------+--------+--------+--------+--------+--------+--------+--------+
|      1 | 语文     |     80 |     31 | 64.50  | 66.67% | 66.67% | 33.33% | 0.00%  |
|      2 | 数学     |     90 |     30 | 72.67  | 83.33% | 16.67% | 66.67% | 16.67% |
|      3 | 英语     |     99 |     34 | 69.33  | 66.67% | 16.67% | 16.67% | 33.33% |
+--------+----------+--------+--------+--------+--------+--------+--------+--------+

 

19、按各科成绩进行排序，并显示排名

select    (@i := case when @pre_group_id = c_id then @i + 1 else 1 end) as rank,    (@pre_group_id := c_id) as c_id,    c_name,s_id,s_name,s_scorefrom (select @i := 0, @pre_group_id := 1) varcross join (    select c.c_id,c.c_name,s.s_id,s.s_name,s_score    from score sc    inner join student s on sc.s_id = s.s_id    inner join course c on sc.c_id = c.c_id    group by c.c_id,s.s_id    order by c.c_id,s_score desc) t1;

+------+------+--------+------+--------+---------+
| rank | c_id | c_name | s_id | s_name | s_score |
+------+------+--------+------+--------+---------+
|    1 |    1 | 语文   |    1 | 赵雷   |      80 |
|    2 |    1 | 语文   |    3 | 孙风   |      80 |
|    3 |    1 | 语文   |    5 | 周梅   |      76 |
|    4 |    1 | 语文   |    2 | 钱电   |      70 |
|    5 |    1 | 语文   |    4 | 李云   |      50 |
|    6 |    1 | 语文   |    6 | 吴兰   |      31 |
|    1 |    2 | 数学   |    1 | 赵雷   |      90 |
|    2 |    2 | 数学   |    7 | 郑竹   |      89 |
|    3 |    2 | 数学   |    5 | 周梅   |      87 |
|    4 |    2 | 数学   |    3 | 孙风   |      80 |
|    5 |    2 | 数学   |    2 | 钱电   |      60 |
|    6 |    2 | 数学   |    4 | 李云   |      30 |
|    1 |    3 | 英语   |    1 | 赵雷   |      99 |
|    2 |    3 | 英语   |    7 | 郑竹   |      98 |
|    3 |    3 | 英语   |    3 | 孙风   |      80 |
|    4 |    3 | 英语   |    2 | 钱电   |      65 |
|    5 |    3 | 英语   |    4 | 李云   |      40 |
|    6 |    3 | 英语   |    6 | 吴兰   |      34 |
+------+------+--------+------+--------+---------+

20、查询学生的总成绩并进行排名

select (@i := @i + 1) as rank,t2.*from (select  @i := 0) varcross join (    select s.s_id,s.s_name,sum_score    from student s    inner join (        select s_id,sum(s_score) as sum_score        from score        group by s_id    ) t1    on s.s_id = t1.s_id    order by sum_score desc) t2;

+------+------+--------+-----------+
| rank | s_id | s_name | sum_score |
+------+------+--------+-----------+
|    1 |    1 | 赵雷   | 269       |
|    2 |    3 | 孙风   | 240       |
|    3 |    2 | 钱电   | 195       |
|    4 |    7 | 郑竹   | 187       |
|    5 |    5 | 周梅   | 163       |
|    6 |    4 | 李云   | 120       |
|    7 |    6 | 吴兰   | 65        |
+------+------+--------+-----------+

21、查询不同老师所教不同课程平均分从高到低显示

select t.t_id,t.t_name,c.c_id,c.c_name,round(avg(s_score), 2) as avg_scorefrom score scinner join course c on sc.c_id = c.c_idinner join teacher t on t.t_id = c.t_idgroup by t.t_id,c.c_idorder by t.t_id,avg_score desc;

+------+--------+------+--------+-----------+
| t_id | t_name | c_id | c_name | avg_score |
+------+--------+------+--------+-----------+
|    1 | 张三   |    2 | 数学   | 72.67     |
|    2 | 李四   |    1 | 语文   | 64.50     |
|    3 | 王五   |    3 | 英语   | 69.33     |
+------+--------+------+--------+-----------+

22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩

select *from (    select        (@i := case when @pre_group_id = c_id then @i + 1 else 1 end) as rank,        (@pre_group_id := c_id) as c_id,        c_name,s_id,s_name,s_birth,s_sex,s_score    from (select @i := 0, @pre_group_id := 1) var    cross join (        select c.c_id,c.c_name,s.*,s_score        from score sc        inner join student s on sc.s_id = s.s_id        inner join course c on sc.c_id = c.c_id        group by c.c_id,s.s_id        order by c.c_id,s_score desc    ) t1) t2where rank in (2,3);

+------+------+--------+------+--------+------------+-------+---------+
| rank | c_id | c_name | s_id | s_name | s_birth    | s_sex | s_score |
+------+------+--------+------+--------+------------+-------+---------+
|    2 |    1 | 语文   |    3 | 孙风   | 1990-05-20 | 男    |      80 |
|    3 |    1 | 语文   |    5 | 周梅   | 1991-12-01 | 女    |      76 |
|    2 |    2 | 数学   |    7 | 郑竹   | 1989-07-01 | 女    |      89 |
|    3 |    2 | 数学   |    5 | 周梅   | 1991-12-01 | 女    |      87 |
|    2 |    3 | 英语   |    7 | 郑竹   | 1989-07-01 | 女    |      98 |
|    3 |    3 | 英语   |    3 | 孙风   | 1990-05-20 | 男    |      80 |
+------+------+--------+------+--------+------------+-------+---------+

23、统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比

select    c.c_id as 课程编号,c.c_name as 课程名称,    sum(case when s_score between 85 and 100 then 1 else 0 end) as '[100-85]',    concat(round(sum(case when s_score between 85 and 100 then 1 else 0 end) / count(*) * 100, 2), '%') as 百分比,    sum(case when s_score between 70 and 85 then 1 else 0 end) as '[85-70]',    concat(round(sum(case when s_score between 70 and 85 then 1 else 0 end) / count(*) * 100, 2), '%') as 百分比,    sum(case when s_score between 60 and 70 then 1 else 0 end) as '[70-60]',    concat(round(sum(case when s_score between 60 and 70 then 1 else 0 end) / count(*) * 100, 2), '%') as 百分比,    sum(case when s_score between 0 and 60 then 1 else 0 end) as '[0-60]',    concat(round(sum(case when s_score between 0 and 60 then 1 else 0 end) / count(*) * 100, 2), '%') as 百分比from course cinner join score scon c.c_id = sc.c_idgroup by c.c_id;

+----------+----------+----------+--------+---------+--------+---------+--------+--------+--------+
| 课程编号 | 课程名称 | [100-85] | 百分比 | [85-70] | 百分比 | [70-60] | 百分比 | [0-60] | 百分比 |
+----------+----------+----------+--------+---------+--------+---------+--------+--------+--------+
|        1 | 语文     | 0        | 0.00%  | 4       | 66.67% | 1       | 16.67% | 2      | 33.33% |
|        2 | 数学     | 3        | 50.00% | 1       | 16.67% | 1       | 16.67% | 2      | 33.33% |
|        3 | 英语     | 2        | 33.33% | 1       | 16.67% | 1       | 16.67% | 2      | 33.33% |
+----------+----------+----------+--------+---------+--------+---------+--------+--------+--------+

24、查询学生平均成绩及其名次

select (@i := @i + 1) as rank,t2.*from (select  @i := 0) varcross join (    select s.s_id,s.s_name,avg_score    from student s    inner join (        select s_id,round(avg(s_score), 2) as avg_score        from score        group by s_id    ) t1    on s.s_id = t1.s_id    order by avg_score desc) t2;

+------+------+--------+-----------+
| rank | s_id | s_name | avg_score |
+------+------+--------+-----------+
|    1 |    7 | 郑竹   | 93.50     |
|    2 |    1 | 赵雷   | 89.67     |
|    3 |    5 | 周梅   | 81.50     |
|    4 |    3 | 孙风   | 80.00     |
|    5 |    2 | 钱电   | 65.00     |
|    6 |    4 | 李云   | 40.00     |
|    7 |    6 | 吴兰   | 32.50     |
+------+------+--------+-----------+

25、查询各科成绩前三名的记录

方法 1：内外关联

select c.c_id,c.c_name,s.s_id,s.s_name,s_scorefrom (    select *    from score sc    where (        select count(*)        from score sc1        where sc.c_id = sc1.c_id        and sc.s_score < sc1.s_score    ) < 3)t1inner join student s on t1.s_id = s.s_id inner join course c on t1.c_id = c.c_id order by c.c_id,s_score desc;

+------+--------+------+--------+---------+
| c_id | c_name | s_id | s_name | s_score |
+------+--------+------+--------+---------+
|    1 | 语文   |    1 | 赵雷   |      80 |
|    1 | 语文   |    3 | 孙风   |      80 |
|    1 | 语文   |    5 | 周梅   |      76 |
|    2 | 数学   |    1 | 赵雷   |      90 |
|    2 | 数学   |    7 | 郑竹   |      89 |
|    2 | 数学   |    5 | 周梅   |      87 |
|    3 | 英语   |    1 | 赵雷   |      99 |
|    3 | 英语   |    7 | 郑竹   |      98 |
|    3 | 英语   |    3 | 孙风   |      80 |
+------+--------+------+--------+---------+

方法 2：序号筛选

select *from (    select        (@i := case when @pre_group_id = c_id then @i + 1 else 1 end) as rank,        (@pre_group_id := c_id) as c_id,        c_name,s_id,s_name,s_score    from (select @i := 0, @pre_group_id := 1) var    cross join (        select c.c_id,c.c_name,s.s_id,s.s_name,s_score        from score sc        inner join student s on sc.s_id = s.s_id        inner join course c on sc.c_id = c.c_id        group by c.c_id,s.s_id        order by c.c_id,s_score desc    ) t1) t2where rank <= 3;

+------+------+--------+------+--------+---------+
| rank | c_id | c_name | s_id | s_name | s_score |
+------+------+--------+------+--------+---------+
|    1 |    1 | 语文   |    1 | 赵雷   |      80 |
|    2 |    1 | 语文   |    3 | 孙风   |      80 |
|    3 |    1 | 语文   |    5 | 周梅   |      76 |
|    1 |    2 | 数学   |    1 | 赵雷   |      90 |
|    2 |    2 | 数学   |    7 | 郑竹   |      89 |
|    3 |    2 | 数学   |    5 | 周梅   |      87 |
|    1 |    3 | 英语   |    1 | 赵雷   |      99 |
|    2 |    3 | 英语   |    7 | 郑竹   |      98 |
|    3 |    3 | 英语   |    3 | 孙风   |      80 |
+------+------+--------+------+--------+---------+

26、查询每门课程被选修的学生数

select c.c_id,c.c_name,cnt_studentfrom course cinner join (    select c_id,count(*) as cnt_student    from score    group by c_id) t1on c.c_id = t1.c_id;

+------+--------+-------------+
| c_id | c_name | cnt_student |
+------+--------+-------------+
|    1 | 语文   |           6 |
|    2 | 数学   |           6 |
|    3 | 英语   |           6 |
+------+--------+-------------+

27、查询出只有两门课程的全部学生的学号和姓名

select s_id,s_namefrom studentwhere s_id in (    select s_id    from score    group by s_id    having count(*) = 2);

+------+--------+
| s_id | s_name |
+------+--------+
|    5 | 周梅   |
|    6 | 吴兰   |
|    7 | 郑竹   |
+------+--------+

28、查询男生、女生人数

select s_sex,count(*) as cnt_sexfrom studentgroup by s_sex;

+-------+---------+
| s_sex | cnt_sex |
+-------+---------+
| 女    |       4 |
| 男    |       4 |
+-------+---------+

29、查询名字中含有"风"字的学生信息

select *from studentwhere s_name like '%风%';

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    3 | 孙风   | 1990-05-20 | 男    |
+------+--------+------------+-------+

30、查询同名同性学生名单，并统计同名人数

select *,count(*) as cnt_studentfrom studentgroup by s_name,s_sexhaving cnt_student > 1;

+-----------+
| Empty set |
+-----------+

31、查询1990年出生的学生名单

select *from studentwhere year(s_birth) = '1990';

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 赵雷   | 1990-01-01 | 男    |
|    2 | 钱电   | 1990-12-21 | 男    |
|    3 | 孙风   | 1990-05-20 | 男    |
|    4 | 李云   | 1990-08-06 | 男    |
|    8 | 王菊   | 1990-01-20 | 女    |
+------+--------+------------+-------+

32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

select c.c_id,c.c_name,avg_scorefrom course cinner join (    select c_id,round(avg(s_score), 2) as avg_score    from score    group by c_id) t1on c.c_id = t1.c_idorder by avg_score desc,c.c_id;

+------+--------+-----------+
| c_id | c_name | avg_score |
+------+--------+-----------+
|    2 | 数学   | 72.67     |
|    3 | 英语   | 69.33     |
|    1 | 语文   | 64.50     |
+------+--------+-----------+

33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩

select s.s_id,s.s_name,avg_scorefrom student sinner join (    select s_id,round(avg(s_score), 2) as avg_score    from score    group by s_id    having avg_score >= 85) t1on s.s_id = t1.s_id;

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    1 | 赵雷   | 89.67     |
|    7 | 郑竹   | 93.50     |
+------+--------+-----------+

 

34、查询课程名称为"数学"，且分数低于60的学生姓名和分数

select s_name,s_scorefrom student sinner join (    select s_id,s_score    from score sc    inner join course c on sc.c_id = c.c_id    where c_name = '数学'    and s_score < 60) t1on s.s_id = t1.s_id;

+--------+---------+
| s_name | s_score |
+--------+---------+
| 李云   |      30 |
+--------+---------+

35、查询所有学生的课程及分数情况

select    s.s_id,s.s_name,    sum(case c_id when 1 then s_score else 0 end) as 语文,    sum(case c_id when 2 then s_score else 0 end) as 数学,    sum(case c_id when 3 then s_score else 0 end) as 英语from student sleft join score sc on s.s_id = sc.s_idgroup by s.s_id;

+------+--------+------+------+------+
| s_id | s_name | 语文 | 数学 | 英语 |
+------+--------+------+------+------+
|    1 | 赵雷   | 80   | 90   | 99   |
|    2 | 钱电   | 70   | 60   | 65   |
|    3 | 孙风   | 80   | 80   | 80   |
|    4 | 李云   | 50   | 30   | 40   |
|    5 | 周梅   | 76   | 87   | 0    |
|    6 | 吴兰   | 31   | 0    | 34   |
|    7 | 郑竹   | 0    | 89   | 98   |
|    8 | 王菊   | 0    | 0    | 0    |
+------+--------+------+------+------+

36、查询任何一门课程成绩在70分以上的学生姓名、课程名称和分数

select s_name,c_name,s_scorefrom score scinner join student s on sc.s_id =  s.s_idinner join course c on sc.c_id = c.c_idwhere s_score > 70group by s.s_id;

+--------+--------+---------+
| s_name | c_name | s_score |
+--------+--------+---------+
| 赵雷   | 语文   |      80 |
| 孙风   | 语文   |      80 |
| 周梅   | 语文   |      76 |
| 郑竹   | 数学   |      89 |
+--------+--------+---------+

37、查询课程不及格的学生

select s.s_id,s.s_name,c.c_id,c.c_name,s_scorefrom score scinner join student s on sc.s_id =  s.s_idinner join course c on sc.c_id = c.c_idwhere s_score < 60;

+------+--------+------+--------+---------+
| s_id | s_name | c_id | c_name | s_score |
+------+--------+------+--------+---------+
|    4 | 李云   |    1 | 语文   |      50 |
|    4 | 李云   |    2 | 数学   |      30 |
|    4 | 李云   |    3 | 英语   |      40 |
|    6 | 吴兰   |    1 | 语文   |      31 |
|    6 | 吴兰   |    3 | 英语   |      34 |
+------+--------+------+--------+---------+

38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名

select s.s_id,s.s_namefrom student swhere s_id in (    select s_id    from score    where c_id = 1    and s_score >= 80);

+------+--------+
| s_id | s_name |
+------+--------+
|    1 | 赵雷   |
|    3 | 孙风   |
+------+--------+

39、求每门课程的学生人数

select c.c_id,c.c_name,cnt_studentfrom course cinner join (    select c_id,count(*) as cnt_student    from score    group by c_id) t1on c.c_id = t1.c_id;

+------+--------+-------------+
| c_id | c_name | cnt_student |
+------+--------+-------------+
|    1 | 语文   |           6 |
|    2 | 数学   |           6 |
|    3 | 英语   |           6 |
+------+--------+-------------+

40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩

select s.*,s_score as max_scorefrom student sinner join (    select s_id,s_score    from score sc    inner join (        select c_id        from course c        inner join teacher t on c.t_id = t.t_id        where t_name = '张三'    ) t1    on sc.c_id = t1.c_id    order by s_score desc    limit 1) t2on s.s_id = t2.s_id;

+------+--------+------------+-------+-----------+
| s_id | s_name | s_birth    | s_sex | max_score |
+------+--------+------------+-------+-----------+
|    1 | 赵雷   | 1990-01-01 | 男    |        90 |
+------+--------+------------+-------+-----------+

41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

select *from scorewhere s_score in (    select s_score    from score    group by s_score    having count(*) > 1);

+------+------+---------+
| s_id | c_id | s_score |
+------+------+---------+
|    1 |    1 |      80 |
|    3 |    1 |      80 |
|    3 |    2 |      80 |
|    3 |    3 |      80 |
+------+------+---------+

42、查询每门课程成绩最好的前三名

方法 1：内外关联

select c.c_id,c.c_name,s.s_id,s.s_name,s_scorefrom (    select *    from score sc    where (        select count(*)        from score sc1        where sc.c_id = sc1.c_id        and sc.s_score < sc1.s_score    ) < 3) t1inner join student s on t1.s_id = s.s_idinner join course c on t1.c_id = c.c_idorder by c.c_id,s_score desc;

+------+--------+------+--------+---------+
| c_id | c_name | s_id | s_name | s_score |
+------+--------+------+--------+---------+
|    1 | 语文   |    1 | 赵雷   |      80 |
|    1 | 语文   |    3 | 孙风   |      80 |
|    1 | 语文   |    5 | 周梅   |      76 |
|    2 | 数学   |    1 | 赵雷   |      90 |
|    2 | 数学   |    7 | 郑竹   |      89 |
|    2 | 数学   |    5 | 周梅   |      87 |
|    3 | 英语   |    1 | 赵雷   |      99 |
|    3 | 英语   |    7 | 郑竹   |      98 |
|    3 | 英语   |    3 | 孙风   |      80 |
+------+--------+------+--------+---------+

方法 2：序号筛选

select *from (    select        (@i := case when @pre_group_id = c_id then @i + 1 else 1 end) as rank,        (@pre_group_id := c_id) as c_id,        c_name,s_id,s_name,s_score    from (select @i := 0, @pre_group_id := 1) var    cross join (        select c.c_id,c.c_name,s.s_id,s.s_name,s_score        from score sc        inner join student s on sc.s_id = s.s_id        inner join course c on sc.c_id = c.c_id        group by c.c_id,s.s_id        order by c.c_id,s_score desc    ) t1) t2where rank <= 3;

+------+------+--------+------+--------+---------+
| rank | c_id | c_name | s_id | s_name | s_score |
+------+------+--------+------+--------+---------+
|    1 |    1 | 语文   |    1 | 赵雷   |      80 |
|    2 |    1 | 语文   |    3 | 孙风   |      80 |
|    3 |    1 | 语文   |    5 | 周梅   |      76 |
|    1 |    2 | 数学   |    1 | 赵雷   |      90 |
|    2 |    2 | 数学   |    7 | 郑竹   |      89 |
|    3 |    2 | 数学   |    5 | 周梅   |      87 |
|    1 |    3 | 英语   |    1 | 赵雷   |      99 |
|    2 |    3 | 英语   |    7 | 郑竹   |      98 |
|    3 |    3 | 英语   |    3 | 孙风   |      80 |
+------+------+--------+------+--------+---------+

43、统计每门课程的学生选修人数（超过5人的课程才统计）

– 要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

select c.c_id,cnt_studentfrom course cinner join (    select c_id,count(*) as cnt_student    from score    group by c_id    having cnt_student > 5) t1on c.c_id = t1.c_idorder by cnt_student desc,c.c_id;

+------+-------------+
| c_id | cnt_student |
+------+-------------+
|    1 |           6 |
|    2 |           6 |
|    3 |           6 |
+------+-------------+

44、检索至少选修两门课程的学生学号

select s_idfrom scoregroup by s_idhaving count(*) >= 2;

+------+
| s_id |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
|    6 |
|    7 |
+------+

查询选修了全部课程的学生信息

select *from studentwhere s_id in (    select s_id    from score    group by s_id    having count(*) = (        select count(*) from course    ));

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 赵雷   | 1990-01-01 | 男    |
|    2 | 钱电   | 1990-12-21 | 男    |
|    3 | 孙风   | 1990-05-20 | 男    |
|    4 | 李云   | 1990-08-06 | 男    |
+------+--------+------------+-------+

46、查询各学生的年龄(周岁)

– 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

select    s_id,s_name,s_birth,    if (        month(current_date()) < month(s_birth) or (month(current_date()) = month(s_birth) and day(current_date()) < day(s_birth)),        year(current_date()) - year(s_birth) -1,        year(current_date()) - year(s_birth)    )    as s_agefrom student;

47、查询本周过生日的学生

select *from studentwhere    datediff(concat(year(current_date()), date_fORMat(s_birth, '-%m-%d')), current_date())    between 0 and 7or    datediff(concat(year(current_date()) + 1, date_format(s_birth, '-%m-%d')), current_date())    between 0 and 7;

48、查询下周过生日的学生

select *from studentwhere    datediff(concat(year(current_date()), date_format(s_birth, '-%m-%d')), current_date())    between 7 and 14or    datediff(concat(year(current_date()) + 1, date_format(s_birth, '-%m-%d')), current_date())    between 7 and 14;

查询本月过生日的学生

select *from studentwhere month(s_birth) = month(current_date());

查询12月份过生日的学生

select *from studentwhere month(s_birth) = 12;

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    2 | 钱电   | 1990-12-21 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
+------+--------+------------+-------+

来源地址：https://blog.csdn.net/AL_K_ZN/article/details/131549291