MySQL 經典練習 50 題（完美解答版）

原創 GodSuzzZ 2020-06-27 20:55

MySQL 經典練習 50 題（完美解答版）

創建數據庫和表

 

數據庫

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

 

學生表 student

創建學生表 student

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

插入學生數據

insert into student values
(1,'趙雷','1990-01-01','男'),
(2,'錢電','1990-12-21','男'),
(3,'孫風','1990-05-20','男'),
(4,'李雲','1990-08-06','男'),
(5,'周梅','1991-12-01','女'),
(6,'吳蘭','1992-03-01','女'),
(7,'鄭竹','1989-07-01','女'),
(8,'王菊','1990-01-20','女');

 

課程表 course

創建課程表 course

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

插入課程數據

insert into course values
(1,'語文',2),
(2,'數學',1),
(3,'英語',3);

 

教師表 teacher

創建教師表 teacher

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

插入教師數據

insert into teacher values
(1,'張三'),
(2,'李四'),
(3,'王五');

 

成績表 score

創建成績表 score

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

插入成績數據

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);

 

表關係

在這裏插入圖片描述
 

經典練習 50 題

 

1、查詢"01"課程比"02"課程成績高的學生的信息及課程分數

select s.*,sc1.s_score as score_01,sc2.s_score as score_02
from student s
inner join (
	select * from score where c_id = 1
) sc1
on s.s_id = sc1.s_id
inner join (
	select * from score where c_id = 2
) sc2
on s.s_id = sc2.s_id
where sc1.s_score > sc2.s_score;

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

 

2、查詢"01"課程比"02"課程成績低的學生的信息及課程分數

select s.*,sc1.s_score as score_01,sc2.s_score as score_02
from student s
inner join (
	select * from score where c_id = 1
) sc1
on s.s_id = sc1.s_id
inner join (
	select * from score where c_id = 2
) sc2
on s.s_id = sc2.s_id
where sc1.s_score < sc2.s_score;

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

 

3、查詢平均成績大於等於60分的同學的學生編號和學生姓名和平均成績

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

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    1 | 趙雷   | 89.67     |
|    2 | 錢電   | 65.00     |
|    3 | 孫風   | 80.00     |
|    5 | 周梅   | 81.50     |
|    7 | 鄭竹   | 93.50     |
+------+--------+-----------+

 

4、查詢平均成績小於60分的同學的學生編號和學生姓名和平均成績(包括有成績的和無成績的)

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

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    4 | 李雲   | 40.00     |
|    6 | 吳蘭   | 32.50     |
|    8 | 王菊   | 0.00      |
+------+--------+-----------+

 

5、查詢所有同學的學生編號、學生姓名、選課總數、所有課程的總成績

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

+------+--------+------------+-----------+
| s_id | s_name | cnt_course | sum_score |
+------+--------+------------+-----------+
|    1 | 趙雷   |          3 | 269       |
|    2 | 錢電   |          3 | 195       |
|    3 | 孫風   |          3 | 240       |
|    4 | 李雲   |          3 | 120       |
|    5 | 周梅   |          2 | 163       |
|    6 | 吳蘭   |          2 | 65        |
|    7 | 鄭竹   |          2 | 187       |
|    8 | 王菊   |          0 | 0         |
+------+--------+------------+-----------+

 

6、查詢"李"姓老師的數量

select count(*) as cnt_name_li
from teacher
where t_name like '李%';

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

 

7、詢學過"張三"老師授課的同學的信息

select s.*
from student s
where 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 = '張三'
	) t1
	on sc.c_id = t1.c_id
);

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 趙雷   | 1990-01-01 | 男    |
|    2 | 錢電   | 1990-12-21 | 男    |
|    3 | 孫風   | 1990-05-20 | 男    |
|    4 | 李雲   | 1990-08-06 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
|    7 | 鄭竹   | 1989-07-01 | 女    |
+------+--------+------------+-------+

 

8、查詢沒學過"張三"老師授課的同學的信息

select s.*
from student s
where 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 = '張三'
	) t1
	on sc.c_id = t1.c_id
);

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

 

9、查詢學過編號爲"01"並且也學過編號爲"02"的課程的同學的信息

select s.*
from student s
where 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 | 趙雷   | 1990-01-01 | 男    |
|    2 | 錢電   | 1990-12-21 | 男    |
|    3 | 孫風   | 1990-05-20 | 男    |
|    4 | 李雲   | 1990-08-06 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
+------+--------+------------+-------+

 

10、查詢學過編號爲"01"但是沒有學過編號爲"02"的課程的同學的信息

select s.*
from student s
where 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 | 吳蘭   | 1992-03-01 | 女    |
+------+--------+------------+-------+

 

11、查詢沒有學全所有課程的同學的信息

select *
from student
where 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 | 吳蘭   | 1992-03-01 | 女    |
|    7 | 鄭竹   | 1989-07-01 | 女    |
|    8 | 王菊   | 1990-01-20 | 女    |
+------+--------+------------+-------+

 

12、查詢至少有一門課與學號爲"01"的同學所學相同的同學的信息

select *
from student
where 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 | 趙雷   | 1990-01-01 | 男    |
|    2 | 錢電   | 1990-12-21 | 男    |
|    3 | 孫風   | 1990-05-20 | 男    |
|    4 | 李雲   | 1990-08-06 | 男    |
|    5 | 周梅   | 1991-12-01 | 女    |
|    6 | 吳蘭   | 1992-03-01 | 女    |
|    7 | 鄭竹   | 1989-07-01 | 女    |
+------+--------+------------+-------+

 

13、查詢和"01"號的同學學習的課程完全相同的其他同學的信息

select *
from student
where 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_idhaving count(*) = (
		select count(*) from score where s_id = 1
	 )
);

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    2 | 錢電   | 1990-12-21 | 男    |
|    3 | 孫風   | 1990-05-20 | 男    |
|    4 | 李雲   | 1990-08-06 | 男    |
+------+--------+------------+-------+

 

14、查詢沒學過"張三"老師講授的任一門課程的學生姓名

select s_name
from student
where 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 = '張三'
	) t1
	on sc.c_id = t1.c_id
);

+--------+
| s_name |
+--------+
| 吳蘭   |
| 王菊   |
+--------+

 

15、查詢兩門及其以上不及格課程的同學的學號，姓名及其平均成績

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

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    4 | 李雲   | 40.00     |
|    6 | 吳蘭   | 32.50     |
+------+--------+-----------+

 

16、檢索"01"課程分數小於60，按分數降序排列的學生信息

select s.*,s_score as score_01
from student s
inner join (
	select s_id,s_score
	from score
	where c_id = 1
	and s_score < 60
) t1
on s.s_id = t1.s_id
order by score_01 desc;

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

 

17、按平均成績從高到低顯示所有學生的所有課程的成績以及平均成績

select
	s.s_id as 學號,s.s_name as 姓名,
	sum(case c_id when 1 then s_score else 0 end) as 語文,
	sum(case c_id when 2 then s_score else 0 end) as 數學,
	sum(case c_id when 3 then s_score else 0 end) as 英語,
	ifnull(round(avg(s_score), 2), 0) as 平均成績
from student s
left join score sc on s.s_id = sc.s_id
group by s.s_id
order by 平均成績 desc;

+------+------+------+------+------+----------+
| 學號 | 姓名 | 語文 | 數學 | 英語 | 平均成績 |
+------+------+------+------+------+----------+
|    7 | 鄭竹 | 0    | 89   | 98   | 93.50    |
|    1 | 趙雷 | 80   | 90   | 99   | 89.67    |
|    5 | 周梅 | 76   | 87   | 0    | 81.50    |
|    3 | 孫風 | 80   | 80   | 80   | 80.00    |
|    2 | 錢電 | 70   | 60   | 65   | 65.00    |
|    4 | 李雲 | 50   | 30   | 40   | 40.00    |
|    6 | 吳蘭 | 31   | 0    | 34   | 32.50    |
|    8 | 王菊 | 0    | 0    | 0    | 0.00     |
+------+------+------+------+------+----------+

 

18、查詢各科成績最高分、最低分和平均分，以如下形式顯示：

課程ID，課程name，最高分，最低分，平均分，及格率，中等率，優良率，優秀率
– 及格爲>=60，中等爲：70-80，優良爲：80-90，優秀爲：>=90

select
    c.c_id as 課程ID,c.c_name as 課程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 優良率,
	concat(round(sum(case when s_score >= 90 then 1 else 0 end) / count(*) * 100, 2), '%') as 優秀率
from course c
inner join score s on c.c_id = s.c_id
group by c.c_id;

+--------+----------+--------+--------+--------+--------+--------+--------+--------+
| 課程ID | 課程name | 最高分 | 最低分 | 平均分 | 及格率 | 中等率 | 優良率 | 優秀率 |
+--------+----------+--------+--------+--------+--------+--------+--------+--------+
|      1 | 語文     |     80 |     31 | 64.50  | 66.67% | 66.67% | 33.33% | 0.00%  |
|      2 | 數學     |     90 |     30 | 72.67  | 83.33% | 16.67% | 66.67% | 16.67% |
|      3 | 英語     |     99 |     34 | 69.33  | 66.67% | 16.67% | 16.67% | 33.33% |
+--------+----------+--------+--------+--------+--------+--------+--------+--------+

 

19、按各科成績進行排序，並顯示排名

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_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;

+------+------+--------+------+--------+---------+
| rank | c_id | c_name | s_id | s_name | s_score |
+------+------+--------+------+--------+---------+
|    1 |    1 | 語文   |    1 | 趙雷   |      80 |
|    2 |    1 | 語文   |    3 | 孫風   |      80 |
|    3 |    1 | 語文   |    5 | 周梅   |      76 |
|    4 |    1 | 語文   |    2 | 錢電   |      70 |
|    5 |    1 | 語文   |    4 | 李雲   |      50 |
|    6 |    1 | 語文   |    6 | 吳蘭   |      31 |
|    1 |    2 | 數學   |    1 | 趙雷   |      90 |
|    2 |    2 | 數學   |    7 | 鄭竹   |      89 |
|    3 |    2 | 數學   |    5 | 周梅   |      87 |
|    4 |    2 | 數學   |    3 | 孫風   |      80 |
|    5 |    2 | 數學   |    2 | 錢電   |      60 |
|    6 |    2 | 數學   |    4 | 李雲   |      30 |
|    1 |    3 | 英語   |    1 | 趙雷   |      99 |
|    2 |    3 | 英語   |    7 | 鄭竹   |      98 |
|    3 |    3 | 英語   |    3 | 孫風   |      80 |
|    4 |    3 | 英語   |    2 | 錢電   |      65 |
|    5 |    3 | 英語   |    4 | 李雲   |      40 |
|    6 |    3 | 英語   |    6 | 吳蘭   |      34 |
+------+------+--------+------+--------+---------+

 

20、查詢學生的總成績並進行排名

select (@i := @i + 1) as rank,t2.*
from (select  @i := 0) var
cross 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 | 趙雷   | 269       |
|    2 |    3 | 孫風   | 240       |
|    3 |    2 | 錢電   | 195       |
|    4 |    7 | 鄭竹   | 187       |
|    5 |    5 | 周梅   | 163       |
|    6 |    4 | 李雲   | 120       |
|    7 |    6 | 吳蘭   | 65        |
+------+------+--------+-----------+

 

21、查詢不同老師所教不同課程平均分從高到低顯示

select t.t_id,t.t_name,c.c_id,c.c_name,round(avg(s_score), 2) as avg_score
from score sc
inner join course c on sc.c_id = c.c_id
inner join teacher t on t.t_id = c.t_id
group by t.t_id,c.c_id
order by t.t_id,avg_score desc;

+------+--------+------+--------+-----------+
| t_id | t_name | c_id | c_name | avg_score |
+------+--------+------+--------+-----------+
|    1 | 張三   |    2 | 數學   | 72.67     |
|    2 | 李四   |    1 | 語文   | 64.50     |
|    3 | 王五   |    3 | 英語   | 69.33     |
+------+--------+------+--------+-----------+

 

22、查詢所有課程的成績第2名到第3名的學生信息及該課程成績

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
) t2
where rank in (2,3);

+------+------+--------+------+--------+------------+-------+---------+
| rank | c_id | c_name | s_id | s_name | s_birth    | s_sex | s_score |
+------+------+--------+------+--------+------------+-------+---------+
|    2 |    1 | 語文   |    3 | 孫風   | 1990-05-20 | 男    |      80 |
|    3 |    1 | 語文   |    5 | 周梅   | 1991-12-01 | 女    |      76 |
|    2 |    2 | 數學   |    7 | 鄭竹   | 1989-07-01 | 女    |      89 |
|    3 |    2 | 數學   |    5 | 周梅   | 1991-12-01 | 女    |      87 |
|    2 |    3 | 英語   |    7 | 鄭竹   | 1989-07-01 | 女    |      98 |
|    3 |    3 | 英語   |    3 | 孫風   | 1990-05-20 | 男    |      80 |
+------+------+--------+------+--------+------------+-------+---------+

 

23、統計各科成績各分數段人數：課程編號,課程名稱,[100-85],[85-70],[70-60],[0-60]及所佔百分比

select
	c.c_id as 課程編號,c.c_name as 課程名稱,
	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 c
inner join score sc
on c.c_id = sc.c_id
group by c.c_id;

+----------+----------+----------+--------+---------+--------+---------+--------+--------+--------+
| 課程編號 | 課程名稱 | [100-85] | 百分比 | [85-70] | 百分比 | [70-60] | 百分比 | [0-60] | 百分比 |
+----------+----------+----------+--------+---------+--------+---------+--------+--------+--------+
|        1 | 語文     | 0        | 0.00%  | 4       | 66.67% | 1       | 16.67% | 2      | 33.33% |
|        2 | 數學     | 3        | 50.00% | 1       | 16.67% | 1       | 16.67% | 2      | 33.33% |
|        3 | 英語     | 2        | 33.33% | 1       | 16.67% | 1       | 16.67% | 2      | 33.33% |
+----------+----------+----------+--------+---------+--------+---------+--------+--------+--------+

 

24、查詢學生平均成績及其名次

select (@i := @i + 1) as rank,t2.*
from (select  @i := 0) var
cross 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 | 鄭竹   | 93.50     |
|    2 |    1 | 趙雷   | 89.67     |
|    3 |    5 | 周梅   | 81.50     |
|    4 |    3 | 孫風   | 80.00     |
|    5 |    2 | 錢電   | 65.00     |
|    6 |    4 | 李雲   | 40.00     |
|    7 |    6 | 吳蘭   | 32.50     |
+------+------+--------+-----------+

 

25、查詢各科成績前三名的記錄

方法 1：內外關聯

select c.c_id,c.c_name,s.s_id,s.s_name,s_score
from (
	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
)
t1
inner 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 | 語文   |    1 | 趙雷   |      80 |
|    1 | 語文   |    3 | 孫風   |      80 |
|    1 | 語文   |    5 | 周梅   |      76 |
|    2 | 數學   |    1 | 趙雷   |      90 |
|    2 | 數學   |    7 | 鄭竹   |      89 |
|    2 | 數學   |    5 | 周梅   |      87 |
|    3 | 英語   |    1 | 趙雷   |      99 |
|    3 | 英語   |    7 | 鄭竹   |      98 |
|    3 | 英語   |    3 | 孫風   |      80 |
+------+--------+------+--------+---------+

方法 2：序號篩選

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
) t2
where rank <= 3;

+------+------+--------+------+--------+---------+
| rank | c_id | c_name | s_id | s_name | s_score |
+------+------+--------+------+--------+---------+
|    1 |    1 | 語文   |    1 | 趙雷   |      80 |
|    2 |    1 | 語文   |    3 | 孫風   |      80 |
|    3 |    1 | 語文   |    5 | 周梅   |      76 |
|    1 |    2 | 數學   |    1 | 趙雷   |      90 |
|    2 |    2 | 數學   |    7 | 鄭竹   |      89 |
|    3 |    2 | 數學   |    5 | 周梅   |      87 |
|    1 |    3 | 英語   |    1 | 趙雷   |      99 |
|    2 |    3 | 英語   |    7 | 鄭竹   |      98 |
|    3 |    3 | 英語   |    3 | 孫風   |      80 |
+------+------+--------+------+--------+---------+

 

26、查詢每門課程被選修的學生數

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

+------+--------+-------------+
| c_id | c_name | cnt_student |
+------+--------+-------------+
|    1 | 語文   |           6 |
|    2 | 數學   |           6 |
|    3 | 英語   |           6 |
+------+--------+-------------+

 

27、查詢出只有兩門課程的全部學生的學號和姓名

select s_id,s_name
from student
where s_id in (
	select s_id
	from score
	group by s_id
	having count(*) = 2
);

+------+--------+
| s_id | s_name |
+------+--------+
|    5 | 周梅   |
|    6 | 吳蘭   |
|    7 | 鄭竹   |
+------+--------+

 

28、查詢男生、女生人數

select s_sex,count(*) as cnt_sex
from student
group by s_sex;

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

 

29、查詢名字中含有"風"字的學生信息

select *
from student
where s_name like '%風%';

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

 

30、查詢同名同性學生名單，並統計同名人數

select *,count(*) as cnt_student
from student
group by s_name,s_sex
having cnt_student > 1;

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

 

31、查詢1990年出生的學生名單

select *
from student
where year(s_birth) = '1990';

+------+--------+------------+-------+
| s_id | s_name | s_birth    | s_sex |
+------+--------+------------+-------+
|    1 | 趙雷   | 1990-01-01 | 男    |
|    2 | 錢電   | 1990-12-21 | 男    |
|    3 | 孫風   | 1990-05-20 | 男    |
|    4 | 李雲   | 1990-08-06 | 男    |
|    8 | 王菊   | 1990-01-20 | 女    |
+------+--------+------------+-------+

 

32、查詢每門課程的平均成績，結果按平均成績降序排列，平均成績相同時，按課程編號升序排列

select c.c_id,c.c_name,avg_score
from course c
inner join (
	select c_id,round(avg(s_score), 2) as avg_score
	from score
	group by c_id
) t1
on c.c_id = t1.c_id
order by avg_score desc,c.c_id;

+------+--------+-----------+
| c_id | c_name | avg_score |
+------+--------+-----------+
|    2 | 數學   | 72.67     |
|    3 | 英語   | 69.33     |
|    1 | 語文   | 64.50     |
+------+--------+-----------+

 

33、查詢平均成績大於等於85的所有學生的學號、姓名和平均成績

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
	having avg_score >= 85
) t1
on s.s_id = t1.s_id;

+------+--------+-----------+
| s_id | s_name | avg_score |
+------+--------+-----------+
|    1 | 趙雷   | 89.67     |
|    7 | 鄭竹   | 93.50     |
+------+--------+-----------+

 

34、查詢課程名稱爲"數學"，且分數低於60的學生姓名和分數

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

+--------+---------+
| s_name | s_score |
+--------+---------+
| 李雲   |      30 |
+--------+---------+

 

35、查詢所有學生的課程及分數情況

select
	s.s_id,s.s_name,
	sum(case c_id when 1 then s_score else 0 end) as 語文,
	sum(case c_id when 2 then s_score else 0 end) as 數學,
	sum(case c_id when 3 then s_score else 0 end) as 英語
from student s
left join score sc on s.s_id = sc.s_id
group by s.s_id;

+------+--------+------+------+------+
| s_id | s_name | 語文 | 數學 | 英語 |
+------+--------+------+------+------+
|    1 | 趙雷   | 80   | 90   | 99   |
|    2 | 錢電   | 70   | 60   | 65   |
|    3 | 孫風   | 80   | 80   | 80   |
|    4 | 李雲   | 50   | 30   | 40   |
|    5 | 周梅   | 76   | 87   | 0    |
|    6 | 吳蘭   | 31   | 0    | 34   |
|    7 | 鄭竹   | 0    | 89   | 98   |
|    8 | 王菊   | 0    | 0    | 0    |
+------+--------+------+------+------+

 

36、查詢任何一門課程成績在70分以上的學生姓名、課程名稱和分數

select s_name,c_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
where s_score > 70
group by s.s_id;

+--------+--------+---------+
| s_name | c_name | s_score |
+--------+--------+---------+
| 趙雷   | 語文   |      80 |
| 孫風   | 語文   |      80 |
| 周梅   | 語文   |      76 |
| 鄭竹   | 數學   |      89 |
+--------+--------+---------+

 

37、查詢課程不及格的學生

select s.s_id,s.s_name,c.c_id,c.c_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
where s_score < 60;

+------+--------+------+--------+---------+
| s_id | s_name | c_id | c_name | s_score |
+------+--------+------+--------+---------+
|    4 | 李雲   |    1 | 語文   |      50 |
|    4 | 李雲   |    2 | 數學   |      30 |
|    4 | 李雲   |    3 | 英語   |      40 |
|    6 | 吳蘭   |    1 | 語文   |      31 |
|    6 | 吳蘭   |    3 | 英語   |      34 |
+------+--------+------+--------+---------+

 

38、查詢課程編號爲01且課程成績在80分以上的學生的學號和姓名

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

+------+--------+
| s_id | s_name |
+------+--------+
|    1 | 趙雷   |
|    3 | 孫風   |
+------+--------+

 

39、求每門課程的學生人數

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

+------+--------+-------------+
| c_id | c_name | cnt_student |
+------+--------+-------------+
|    1 | 語文   |           6 |
|    2 | 數學   |           6 |
|    3 | 英語   |           6 |
+------+--------+-------------+

 

40、查詢選修"張三"老師所授課程的學生中，成績最高的學生信息及其成績

select s.*,s_score as max_score
from student s
inner 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 = '張三'
	) t1
	on sc.c_id = t1.c_id
	order by s_score desc
	limit 1
) t2
on s.s_id = t2.s_id;

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

 

41、查詢不同課程成績相同的學生的學生編號、課程編號、學生成績

select *
from score
where 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、查詢每門課程成績最好的前三名

方法 1：內外關聯

select c.c_id,c.c_name,s.s_id,s.s_name,s_score
from (
	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
) t1
inner 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 | 語文   |    1 | 趙雷   |      80 |
|    1 | 語文   |    3 | 孫風   |      80 |
|    1 | 語文   |    5 | 周梅   |      76 |
|    2 | 數學   |    1 | 趙雷   |      90 |
|    2 | 數學   |    7 | 鄭竹   |      89 |
|    2 | 數學   |    5 | 周梅   |      87 |
|    3 | 英語   |    1 | 趙雷   |      99 |
|    3 | 英語   |    7 | 鄭竹   |      98 |
|    3 | 英語   |    3 | 孫風   |      80 |
+------+--------+------+--------+---------+

方法 2：序號篩選

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
) t2
where rank <= 3;

+------+------+--------+------+--------+---------+
| rank | c_id | c_name | s_id | s_name | s_score |
+------+------+--------+------+--------+---------+
|    1 |    1 | 語文   |    1 | 趙雷   |      80 |
|    2 |    1 | 語文   |    3 | 孫風   |      80 |
|    3 |    1 | 語文   |    5 | 周梅   |      76 |
|    1 |    2 | 數學   |    1 | 趙雷   |      90 |
|    2 |    2 | 數學   |    7 | 鄭竹   |      89 |
|    3 |    2 | 數學   |    5 | 周梅   |      87 |
|    1 |    3 | 英語   |    1 | 趙雷   |      99 |
|    2 |    3 | 英語   |    7 | 鄭竹   |      98 |
|    3 |    3 | 英語   |    3 | 孫風   |      80 |
+------+------+--------+------+--------+---------+

 

43、統計每門課程的學生選修人數（超過5人的課程才統計）

– 要求輸出課程號和選修人數，查詢結果按人數降序排列，若人數相同，按課程號升序排列

select c.c_id,cnt_student
from course c
inner join (
	select c_id,count(*) as cnt_student
	from score
	group by c_id
	having cnt_student > 5
) t1
on c.c_id = t1.c_id
order by cnt_student desc,c.c_id;

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

 

44、檢索至少選修兩門課程的學生學號

select s_id
from score
group by s_id
having count(*) >= 2;

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

 

45、查詢選修了全部課程的學生信息

select *
from student
where 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 | 趙雷   | 1990-01-01 | 男    |
|    2 | 錢電   | 1990-12-21 | 男    |
|    3 | 孫風   | 1990-05-20 | 男    |
|    4 | 李雲   | 1990-08-06 | 男    |
+------+--------+------------+-------+

 

46、查詢各學生的年齡(週歲)

– 按照出生日期來算，當前月日 < 出生年月的月日則，年齡減一

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_age
from student;

 

47、查詢本週過生日的學生

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

 

48、查詢下週過生日的學生

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

 

49、查詢本月過生日的學生

select *
from student
where month(s_birth) = month(current_date());

 

50、查詢12月份過生日的學生

select *
from student
where month(s_birth) = 12;

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