一、基础演练：
1、建库、建表
# 创建数据库
create database mysql_exampleTest;
use mysql_exampleTest;
# 学生表
CREATE TABLE Student(
s_id VARCHAR(20),
s_name VARCHAR(20) NOT NULL DEFAULT '',
s_birth VARCHAR(20) NOT NULL DEFAULT '',
s_sex VARCHAR(10) NOT NULL DEFAULT '',
PRIMARY KEY(s_id)
);
# 课程表
CREATE TABLE Course(
c_id VARCHAR(20),
c_name VARCHAR(20) NOT NULL DEFAULT '',
t_id VARCHAR(20) NOT NULL,
PRIMARY KEY(c_id)
);
# 教师表
CREATE TABLE Teacher(
t_id VARCHAR(20),
t_name VARCHAR(20) NOT NULL DEFAULT '',
PRIMARY KEY(t_id)
);
# 成绩表
CREATE TABLE Score(
s_id VARCHAR(20),
c_id VARCHAR(20),
s_Score INT(3),
PRIMARY KEY(s_id,c_id)
);
2、插入数据：
# 插入学生表测试数据
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
Student表：
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
| 05 | 周梅 | 1991-12-01 | 女 |
| 06 | 吴兰 | 1992-03-01 | 女 |
| 07 | 郑竹 | 1989-07-01 | 女 |
| 08 | 王菊 | 1990-01-20 | 女 |
+------+--------+------------+-------+
# 课程表测试数据
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');
Course表：
+------+--------+------+
| c_id | c_name | t_id |
+------+--------+------+
| 01 | 语文 | 02 |
| 02 | 数学 | 01 |
| 03 | 英语 | 03 |
+------+--------+------+
# 教师表测试数据
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');
Teacher表：
+------+--------+
| t_id | t_name |
+------+--------+
| 01 | 张三 |
| 02 | 李四 |
| 03 | 王五 |
+------+--------+
# 成绩表测试数据
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);
Score表：
+------+------+---------+
| s_id | c_id | s_Score |
+------+------+---------+
| 01 | 01 | 80 |
| 01 | 02 | 90 |
| 01 | 03 | 99 |
| 02 | 01 | 70 |
| 02 | 02 | 60 |
| 02 | 03 | 80 |
| 03 | 01 | 80 |
| 03 | 02 | 80 |
| 03 | 03 | 80 |
| 04 | 01 | 50 |
| 04 | 02 | 30 |
| 04 | 03 | 20 |
| 05 | 01 | 76 |
| 05 | 02 | 87 |
| 06 | 01 | 31 |
| 06 | 03 | 34 |
| 07 | 02 | 89 |
| 07 | 03 | 98 |
+------+------+---------+
3、实战查询50例
# 1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
# 2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
# 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
# 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)
# 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
# 6、查询"李"姓老师的数量
# 7、查询学过"张三"老师授课的同学的信息
# 8、查询没学过"张三"老师授课的同学的信息
# 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
# 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
# 11、查询没有学全所有课程的同学的信息
# 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
# 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
# 14、查询没学过"张三"老师讲授的任一门课程的学生姓名
# 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
# 16、检索"01"课程分数小于60，按分数降序排列的学生信息
# 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，可加round,case when t
# 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
# 19、按各科成绩进行排序，并显示排名(实现不完全)
# 20、查询学生的总成绩并进行排名
# 21、查询不同老师所教不同课程平均分从高到低显示
# 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
# 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],[60-0]及所占百分比
# 24、查询学生平均成绩及其名次
# 25、查询各科成绩前三名的记录
# 26、查询每门课程被选修的学生数
# 27、查询出只有两门课程的全部学生的学号和姓名
# 28、查询男生、女生人数
# 29、查询名字中含有"风"字的学生信息
# 30、查询同名同性学生名单，并统计同名人数
# 31、查询1990年出生的学生名单
# 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
# 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
# 34、查询课程名称为"数学"，且分数低于60的学生姓名和分数
# 35、查询所有学生的课程及分数情况；
# 36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数
# 37、查询不及格的课程
# 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
# 39、求每门课程的学生人数
# 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
# 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
# 42、查询每门功成绩最好的前两名
# 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
# 44、检索至少选修两门课程的学生学号
# 45、查询选修了全部课程的学生信息
# 46、查询各学生的年龄(实岁)
# 47、查询本周过生日的学生
# 48、查询下周过生日的学生(还要排除闰年情况)
# 49、查询本月过生日的学生
# 50、查询下月过生日的学生
================================参考答案================================
# 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 st.*,sc.s_Score as '语文' ,sc2.s_Score '数学'
from Student st
left join Score sc on sc.s_id=st.s_id and sc.c_id='01'
left join Score sc2 on sc2.s_id=st.s_id and sc2.c_id='02'
where sc.s_Score>sc2.s_Score;
+------+--------+------------+-------+------+------+
| s_id | s_name | s_birth | s_sex | 语文 | 数学 |
+------+--------+------------+-------+------+------+
| 02 | 钱电 | 1990-12-21 | 男 | 70 | 60 |
| 04 | 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 st.*,sc.s_Score '语文',sc2.s_Score '数学' from Student st
left join Score sc on sc.s_id=st.s_id and sc.c_id='01'
left join Score sc2 on sc2.s_id=st.s_id and sc2.c_id='02'
where sc.s_Score<sc2.s_Score;
+------+--------+------------+-------+------+------+
| s_id | s_name | s_birth | s_sex | 语文 | 数学 |
+------+--------+------------+-------+------+------+
| 01 | 赵雷 | 1990-01-01 | 男 | 80 | 90 |
| 05 | 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 st.s_id,st.s_name,ROUND(AVG(sc.s_Score),2) cjScore from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id having AVG(sc.s_Score)>=60;
+------+--------+---------+
| s_id | s_name | cjScore |
+------+--------+---------+
| 01 | 赵雷 | 89.67 |
| 02 | 钱电 | 70.00 |
| 03 | 孙风 | 80.00 |
| 05 | 周梅 | 81.50 |
| 07 | 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 st.s_id,st.s_name,(case when ROUND(AVG(sc.s_Score),2) is null then 0 else ROUND(AVG(sc.s_Score)) end ) cjScore from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id having AVG(sc.s_Score)<60 or AVG(sc.s_Score) is NULL;
+------+--------+---------+
| s_id | s_name | cjScore |
+------+--------+---------+
| 04 | 李云 | 33 |
| 06 | 吴兰 | 33 |
| 08 | 王菊 | 0 |
+------+--------+---------+
# 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 st.s_id,st.s_name,count(sc.c_id) '选课总数',(case when sum(sc.s_Score) is null or sum(sc.s_Score)='' then 0 else sum(sc.s_Score) end) '总成绩'
from Student st
left outer join Score sc on st.s_id=sc.s_id
group by st.s_id;
+------+--------+----------+--------+
| s_id | s_name | 选课总数 | 总成绩 |
+------+--------+----------+--------+
| 01 | 赵雷 | 3 | 269 |
| 02 | 钱电 | 3 | 210 |
| 03 | 孙风 | 3 | 240 |
| 04 | 李云 | 3 | 100 |
| 05 | 周梅 | 2 | 163 |
| 06 | 吴兰 | 2 | 65 |
| 07 | 郑竹 | 2 | 187 |
| 08 | 王菊 | 0 | 0 |
+------+--------+----------+--------+
# 6、查询"李"姓老师的数量
select t.t_name,count(t.t_id) from Teacher t
group by t.t_id having t.t_name like "李%";
+--------+----------+
| t_name | count(*) |
+--------+----------+
| 李四 | 1 |
+--------+----------+
# 7、查询学过"张三"老师授课的同学的信息
select st.* from Student st
left join Score sc on sc.s_id=st.s_id
left join Course c on c.c_id=sc.c_id
left join Teacher t on t.t_id=c.t_id
where t.t_name="张三";
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
| 05 | 周梅 | 1991-12-01 | 女 |
| 07 | 郑竹 | 1989-07-01 | 女 |
+------+--------+------------+-------+
# *8、查询没学过"张三"老师授课的同学的信息
-- 张三老师教的课
select c.* from Course c left join Teacher t on t.t_id=c.t_id where t.t_name="张三"
-- 有张三老师课成绩的st.s_id
select sc.s_id from Score sc where sc.c_id in (select c.c_id from Course c left join Teacher t on t.t_id=c.t_id where t.t_name="张三")
-- 不在上面查到的st.s_id的学生信息,即没学过张三老师授课的同学信息
select st.* from Student st where st.s_id not in(
select sc.s_id from Score sc where sc.c_id in (select c.c_id from Course c left join Teacher t on t.t_id=c.t_id where t.t_name="张三")
)
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 06 | 吴兰 | 1992-03-01 | 女 |
| 08 | 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 st.* from Student st
inner join Score sc on sc.s_id = st.s_id
inner join Course c on c.c_id=sc.c_id and c.c_id="01"
where st.s_id in (
select st2.s_id from Student st2
inner join Score sc2 on sc2.s_id = st2.s_id
inner join Course c2 on c2.c_id=sc2.c_id and c2.c_id="02"
)
或
select st.*
from Student st
inner join Score s on st.s_id = s.s_id and s.c_id = '01'
inner join Score s2 on st.s_id=s2.s_id and s2.c_id='02';
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
| 05 | 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 st.* from Student st
inner join Score sc on sc.s_id = st.s_id
inner join Course c on c.c_id=sc.c_id and c.c_id="01"
where st.s_id not in (
select st2.s_id from Student st2
inner join Score sc2 on sc2.s_id = st2.s_id
inner join Course c2 on c2.c_id=sc2.c_id and c2.c_id="02"
);
或
select st.* from Student st
inner join Score sc on sc.s_id = st.s_id and sc.c_id="01"
where st.s_id not in (
select st2.s_id from Student st2
inner join Score sc2 on sc2.s_id = st2.s_id and sc2.c_id="02"
);
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 06 | 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 Student where s_id not in (
select st.s_id from Student st
inner join Score sc on sc.s_id = st.s_id and sc.c_id="01"
where st.s_id in (
select st2.s_id from Student st2
inner join Score sc2 on sc2.s_id = st2.s_id and sc2.c_id="02"
) and st.s_id in (
select st2.s_id from Student st2
inner join Score sc2 on sc2.s_id = st2.s_id and sc2.c_id="03"
));
或
select * from Student
where s_id not in
(select s_id from Score group by s_id having count(c_id)=(select count(*) from Course));
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 05 | 周梅 | 1991-12-01 | 女 |
| 06 | 吴兰 | 1992-03-01 | 女 |
| 07 | 郑竹 | 1989-07-01 | 女 |
| 08 | 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 distinct st.* from Student st
left join Score sc on sc.s_id=st.s_id
where sc.c_id in (
select sc2.c_id from Student st2
left join Score sc2 on sc2.s_id=st2.s_id
where st2.s_id ='01'
);
或
select distinct st.*
from Student st inner join Score s on st.s_id = s.s_id
where s.c_id = any (select c_id from Score where s_id = '01');
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
| 05 | 周梅 | 1991-12-01 | 女 |
| 06 | 吴兰 | 1992-03-01 | 女 |
| 07 | 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 st.* from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id
having group_concat(sc.c_id) =
(
select group_concat(sc2.c_id) from Student st2
left join Score sc2 on sc2.s_id=st2.s_id
where st2.s_id ='01'
);
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
+------+--------+------------+-------+
# 14、查询没学过"张三"老师讲授的任一门课程的学生姓名
select st.s_name from Student st
where st.s_id not in (
select sc.s_id from Score sc
inner join Course c on c.c_id=sc.c_id
inner join Teacher t on t.t_id=c.t_id and t.t_name="张三"
);
或
select s_name from Student
where s_id not in
(select distinct st.s_id from Student st left outer join Score s on st.s_id = s.s_id where s.c_id in
(select c_id from Course where t_id = (select t_id from Teacher where t_name = '张三')));
+--------+
| 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 st.s_id,st.s_name,avg(sc.s_Score) from Student st
left join Score sc on sc.s_id=st.s_id
where sc.s_id in (
select sc.s_id from Score sc
where sc.s_Score<60 or sc.s_Score is NULL
group by sc.s_id having COUNT(sc.s_id)>=2
)
group by st.s_id;
或
select st.s_id, st.s_name, avg(s.s_Score)
from Student st left outer join Score s on st.s_id = s.s_id
where st.s_id in (
select s_id from Score
where s_Score < 60 or s_Score is null
group by s_id having count(s_Score) >= 2
)
group by st.s_id, st.s_name;
+------+--------+----------------+
| s_id | s_name | avg(s.s_Score) |
+------+--------+----------------+
| 04 | 李云 | 33.3333 |
| 06 | 吴兰 | 32.5000 |
+------+--------+----------------+
# 16、检索"01"课程分数小于60，按分数降序排列的学生信息
select st.*,sc.s_Score from Student st
inner join Score sc on sc.s_id=st.s_id and sc.c_id="01" and sc.s_Score<60
order by sc.s_Score desc;
或
select st.*, s.s_Score
from Student st inner join Score s on st.s_id = s.s_id
where s.c_id = '01' and s.s_Score < 60
order by s.s_Score desc;
+------+--------+------------+-------+---------+
| s_id | s_name | s_birth | s_sex | s_Score |
+------+--------+------------+-------+---------+
| 04 | 李云 | 1990-08-06 | 男 | 50 |
| 06 | 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，可加round,case when then else end 使显示更完美
select st.s_id,st.s_name,avg(sc4.s_Score) "平均分",sc.s_Score "语文",sc2.s_Score "数学",sc3.s_Score "英语" from Student st
left join Score sc on sc.s_id=st.s_id and sc.c_id="01"
left join Score sc2 on sc2.s_id=st.s_id and sc2.c_id="02"
left join Score sc3 on sc3.s_id=st.s_id and sc3.c_id="03"
left join Score sc4 on sc4.s_id=st.s_id
group by st.s_id
order by avg(sc4.s_Score) desc;
或
select st.s_id, st.s_name, avg(s.s_Score) '平均成绩', s1.s_Score '语文', s2.s_Score '数学', s3.s_Score '英语'
from Student st
left outer join Score s on st.s_id = s.s_id
left outer join Score s1 on st.s_id = s1.s_id and s1.c_id = '01'
left outer join Score s2 on st.s_id = s2.s_id and s2.c_id = '02'
left outer join Score s3 on st.s_id = s3.s_id and s3.c_id = '03'
group by st.s_id, st.s_name
order by avg(s.s_Score) desc;
+------+--------+----------+------+------+------+
| s_id | s_name | 平均成绩 | 语文 | 数学 | 英语 |
+------+--------+----------+------+------+------+
| 07 | 郑竹 | 93.5000 | NULL | 89 | 98 |
| 01 | 赵雷 | 89.6667 | 80 | 90 | 99 |
| 05 | 周梅 | 81.5000 | 76 | 87 | NULL |
| 03 | 孙风 | 80.0000 | 80 | 80 | 80 |
| 02 | 钱电 | 70.0000 | 70 | 60 | 80 |
| 04 | 李云 | 33.3333 | 50 | 30 | 20 |
| 06 | 吴兰 | 32.5000 | 31 | NULL | 34 |
| 08 | 王菊 | NULL | NULL | NULL | NULL |
+------+--------+----------+------+------+------+
# *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,c.c_name,max(sc.s_Score) "最高分",MIN(sc2.s_Score) "最低分",avg(sc3.s_Score) "平均分"
,((select count(s_id) from Score where s_Score>=60 and c_id=c.c_id )/(select count(s_id) from Score where c_id=c.c_id)) "及格率"
,((select count(s_id) from Score where s_Score>=70 and s_Score<80 and c_id=c.c_id )/(select count(s_id) from Score where c_id=c.c_id)) "中等率"
,((select count(s_id) from Score where s_Score>=80 and s_Score<90 and c_id=c.c_id )/(select count(s_id) from Score where c_id=c.c_id)) "优良率"
,((select count(s_id) from Score where s_Score>=90 and c_id=c.c_id )/(select count(s_id) from Score where c_id=c.c_id)) "优秀率"
from Course c
left join Score sc on sc.c_id=c.c_id
left join Score sc2 on sc2.c_id=c.c_id
left join Score sc3 on sc3.c_id=c.c_id
group by c.c_id;
或
select c.c_id, c.c_name, max(s.s_Score) '最高分', min(s.s_Score) '最低分', avg(s.s_Score) '平均分',
(select count(s_Score)/(select count(s_Score) from Score where c_id = c.c_id )
from Score where c_id = c.c_id and s_Score >= 60) '及格率',
(select count(s_Score)/(select count(s_Score) from Score where c_id = c.c_id )
from Score where c_id = c.c_id and (s_Score between 70 and 79)) '中等率',
(select count(s_Score)/(select count(s_Score) from Score where c_id = c.c_id )
from Score where c_id = c.c_id and (s_Score between 80 and 89)) '优良率',
(select count(s_Score)/(select count(s_Score) from Score where c_id = c.c_id )
from Score where c_id = c.c_id and s_Score >= 90) '优秀率'
from Course c left outer join Score s on c.c_id = s.c_id
group by c.c_id, c.c_name;
+------+--------+--------+--------+---------+--------+--------+--------+--------+
| c_id | c_name | 最高分 | 最低分 | 平均分 | 及格率 | 中等率 | 优良率 | 优秀率 |
+------+--------+--------+--------+---------+--------+--------+--------+--------+
| 01 | 语文 | 80 | 31 | 64.5000 | 0.6667 | 0.3333 | 0.3333 | 0.0000 |
| 02 | 数学 | 90 | 30 | 72.6667 | 0.8333 | 0.0000 | 0.5000 | 0.1667 |
| 03 | 英语 | 99 | 20 | 68.5000 | 0.6667 | 0.0000 | 0.3333 | 0.3333 |
+------+--------+--------+--------+---------+--------+--------+--------+--------+
# *19、按各科成绩进行排序，并显示排名(实现不完全)
# mysql没有rank函数
# 加@Score是为了防止用union all 后打乱了顺序
select c1.s_id,c1.c_id,c1.c_name,@Score:=c1.s_Score,@i:=@i+1 from (select c.c_name,sc.* from Course c
left join Score sc on sc.c_id=c.c_id
where c.c_id="01" order by sc.s_Score desc) c1 ,
(select @i:=0) a
union all
select c2.s_id,c2.c_id,c2.c_name,c2.s_Score,@ii:=@ii+1 from (select c.c_name,sc.* from Course c
left join Score sc on sc.c_id=c.c_id
where c.c_id="02" order by sc.s_Score desc) c2 ,
(select @ii:=0) aa
union all
select c3.s_id,c3.c_id,c3.c_name,c3.s_Score,@iii:=@iii+1 from (select c.c_name,sc.* from Course c
left join Score sc on sc.c_id=c.c_id
where c.c_id="03" order by sc.s_Score desc) c3;
set @iii=0;
或
select a.*
from (select st.s_id, st.s_name, c.c_name, s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '01' and s2.s_Score >= s.s_Score and s2.c_id='01'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
union all
select b.*
from (select st.s_id, st.s_name, c.c_name, s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '02' and s2.s_Score >= s.s_Score and s2.c_id='02'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) b
union all
select c.*
from (select st.s_id, st.s_name, c.c_name, s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '03' and s2.s_Score >= s.s_Score and s2.c_id='03'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) c;
+------+--------+--------+---------+------+
| s_id | s_name | c_name | s_Score | 排名 |
+------+--------+--------+---------+------+
| 01 | 赵雷 | 语文 | 80 | 1 |
| 03 | 孙风 | 语文 | 80 | 1 |
| 05 | 周梅 | 语文 | 76 | 2 |
| 02 | 钱电 | 语文 | 70 | 3 |
| 04 | 李云 | 语文 | 50 | 4 |
| 06 | 吴兰 | 语文 | 31 | 5 |
| 01 | 赵雷 | 数学 | 90 | 1 |
| 07 | 郑竹 | 数学 | 89 | 2 |
| 05 | 周梅 | 数学 | 87 | 3 |
| 03 | 孙风 | 数学 | 80 | 4 |
| 02 | 钱电 | 数学 | 60 | 5 |
| 04 | 李云 | 数学 | 30 | 6 |
| 01 | 赵雷 | 英语 | 99 | 1 |
| 07 | 郑竹 | 英语 | 98 | 2 |
| 02 | 钱电 | 英语 | 80 | 3 |
| 03 | 孙风 | 英语 | 80 | 3 |
| 06 | 吴兰 | 英语 | 34 | 4 |
| 04 | 李云 | 英语 | 20 | 5 |
+------+--------+--------+---------+------+
# 20、查询学生的总成绩并进行排名
select st.s_id,st.s_name
,(case when sum(sc.s_Score) is null then 0 else sum(sc.s_Score) end)
from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id order by sum(sc.s_Score) desc;
或
select st.s_id, st.s_name, (case when sum(s.s_Score) is null then 0 else sum(s.s_Score) end) '总成绩'
from Student st left outer join Score s on st.s_id = s.s_id
group by st.s_id, st.s_name
order by sum(s.s_Score) desc;
+------+--------+--------+
| s_id | s_name | 总成绩 |
+------+--------+--------+
| 01 | 赵雷 | 269 |
| 03 | 孙风 | 240 |
| 02 | 钱电 | 210 |
| 07 | 郑竹 | 187 |
| 05 | 周梅 | 163 |
| 04 | 李云 | 100 |
| 06 | 吴兰 | 65 |
| 08 | 王菊 | 0 |
+------+--------+--------+
# 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_name, avg(s.s_Score) '平均分'
from Teacher t left outer join Course c on t.t_id = c.t_id
left outer join Score s on c.c_id = s.c_id
group by t.t_id, t.t_name, c.c_name
order by avg(s.s_Score) desc;
+------+--------+--------+---------+
| t_id | t_name | c_name | 平均分 |
+------+--------+--------+---------+
| 01 | 张三 | 数学 | 72.6667 |
| 03 | 王五 | 英语 | 68.5000 |
| 02 | 李四 | 语文 | 64.5000 |
+------+--------+--------+---------+
# 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 st.*, c.c_name, s.s_Score
from Student st
left join Score s on st.s_id = s.s_id
left join Course c on s.c_id = c.c_id
where s.c_id = '01' and (
s.s_Score between
(select distinct a.s_Score
from (select s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '01' and s2.s_Score >= s.s_Score and s2.c_id='01'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
where a.排名 = 3)
and
(select distinct a.s_Score
from (select s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '01' and s2.s_Score >= s.s_Score and s2.c_id='01'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
where a.排名 = 2)
)
union all
select st.*, c.c_name, s.s_Score
from Student st
left join Score s on st.s_id = s.s_id
left join Course c on s.c_id = c.c_id
where s.c_id = '02' and (
s.s_Score between
(select distinct a.s_Score
from (select s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '02' and s2.s_Score >= s.s_Score and s2.c_id='02'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
where a.排名 = 3)
and
(select distinct a.s_Score
from (select s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '02' and s2.s_Score >= s.s_Score and s2.c_id='02'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
where a.排名 = 2)
)
union all
select st.*, c.c_name, s.s_Score
from Student st
left join Score s on st.s_id = s.s_id
left join Course c on s.c_id = c.c_id
where s.c_id = '03' and (
s.s_Score between
(select distinct a.s_Score
from (select s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '03' and s2.s_Score >= s.s_Score and s2.c_id='03'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
where a.排名 = 3)
and
(select distinct a.s_Score
from (select s.s_Score, count(distinct s2.s_Score) '排名'
from Score s inner join Student st on s.s_id = st.s_id
inner join Course c on s.c_id = c.c_id, Score s2
where c.c_id = '03' and s2.s_Score >= s.s_Score and s2.c_id='03'
group by st.s_id, st.s_name, c.c_name, s.s_Score
order by s.s_Score desc) a
where a.排名 = 2)
);
+------+--------+------------+-------+--------+---------+
| s_id | s_name | s_birth | s_sex | c_name | s_Score |
+------+--------+------------+-------+--------+---------+
| 02 | 钱电 | 1990-12-21 | 男 | 语文 | 70 |
| 05 | 周梅 | 1991-12-01 | 女 | 语文 | 76 |
| 05 | 周梅 | 1991-12-01 | 女 | 数学 | 87 |
| 07 | 郑竹 | 1989-07-01 | 女 | 数学 | 89 |
| 02 | 钱电 | 1990-12-21 | 男 | 英语 | 80 |
| 03 | 孙风 | 1990-05-20 | 男 | 英语 | 80 |
| 07 | 郑竹 | 1989-07-01 | 女 | 英语 | 98 |
+------+--------+------------+-------+--------+---------+
# *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],[60-0]及所占百分比
select c.c_id,c.c_name
,((select count(1) from Score sc where sc.c_id=c.c_id and sc.s_Score<=100 and sc.s_Score>80)/(select count(1) from Score sc where sc.c_id=c.c_id )) "100-85"
,((select count(1) from Score sc where sc.c_id=c.c_id and sc.s_Score<=85 and sc.s_Score>70)/(select count(1) from Score sc where sc.c_id=c.c_id )) "85-70"
,((select count(1) from Score sc where sc.c_id=c.c_id and sc.s_Score<=70 and sc.s_Score>60)/(select count(1) from Score sc where sc.c_id=c.c_id )) "70-60"
,((select count(1) from Score sc where sc.c_id=c.c_id and sc.s_Score<=60 and sc.s_Score>=0)/(select count(1) from Score sc where sc.c_id=c.c_id )) "60-0"
from Course c order by c.c_id;
+------+--------+--------+--------+--------+--------+
| c_id | c_name | 100-85 | 85-70 | 70-60 | 60-0 |
+------+--------+--------+--------+--------+--------+
| 01 | 语文 | 0.0000 | 0.5000 | 0.1667 | 0.3333 |
| 02 | 数学 | 0.5000 | 0.1667 | 0.0000 | 0.3333 |
| 03 | 英语 | 0.3333 | 0.3333 | 0.0000 | 0.3333 |
+------+--------+--------+--------+--------+--------+
--count(1) 会统计表中的所有的记录数，包含字段为null 的记录。
--count(字段) 会统计该字段在表中出现的次数，忽略字段为null 的情况。即不统计字段为null 的记录。
# 24、查询学生平均成绩及其名次
select a.*, count(distinct b.平均成绩) '名次'
from
(select st.s_id, st.s_name, (case when avg(s.s_Score) is null then 0 else avg(s.s_Score) end) '平均成绩'
from Student st left join Score s on st.s_id=s.s_id
group by st.s_id, st.s_name) a,
(select st.s_id, (case when avg(s.s_Score) is null then 0 else avg(s.s_Score) end) '平均成绩'
from Student st left join Score s on st.s_id=s.s_id
group by st.s_id) b
where a.平均成绩<=b.平均成绩
group by a.s_id
order by a.平均成绩 desc;
+------+--------+----------+------+
| s_id | s_name | 平均成绩 | 名次 |
+------+--------+----------+------+
| 07 | 郑竹 | 93.5000 | 1 |
| 01 | 赵雷 | 89.6667 | 2 |
| 05 | 周梅 | 81.5000 | 3 |
| 03 | 孙风 | 80.0000 | 4 |
| 02 | 钱电 | 70.0000 | 5 |
| 04 | 李云 | 33.3333 | 6 |
| 06 | 吴兰 | 32.5000 | 7 |
| 08 | 王菊 | 0.0000 | 8 |
+------+--------+----------+------+
# 25、查询各科成绩前三名的记录
select a.*
from (
select st.*, c.c_name, s.s_Score
from Student st
left join Score s on st.s_id=s.s_id
left join Course c on c.c_id=s.c_id
where c.c_id='01' and s.s_Score between (
select distinct a1.s_Score
from (
select a2.s_id, a2.s_Score, count(distinct a3.s_Score) '名次'
from Score a2, Score a3
where a2.c_id='01' and a3.c_id='01' and a2.s_Score<=a3.s_Score
group by a2.s_id, a2.s_Score
) a1
where a1.名次=3)
and
(select max(s_Score) from Score where c_id='01')
) a
union all
select b.*
from (
select st.*, c.c_name, s.s_Score
from Student st
left join Score s on st.s_id=s.s_id
left join Course c on c.c_id=s.c_id
where c.c_id='02' and s.s_Score between (
select distinct a1.s_Score
from (
select a2.s_id, a2.s_Score, count(distinct a3.s_Score) '名次'
from Score a2, Score a3
where a2.c_id='02' and a3.c_id='02' and a2.s_Score<=a3.s_Score
group by a2.s_id, a2.s_Score
) a1
where a1.名次=3)
and
(select max(s_Score) from Score where c_id='02')
) b
union all
select c.*
from (
select st.*, c.c_name, s.s_Score
from Student st
left join Score s on st.s_id=s.s_id
left join Course c on c.c_id=s.c_id
where c.c_id='03' and s.s_Score between (
select distinct a1.s_Score
from (
select a2.s_id, a2.s_Score, count(distinct a3.s_Score) '名次'
from Score a2, Score a3
where a2.c_id='03' and a3.c_id='03' and a2.s_Score<=a3.s_Score
group by a2.s_id, a2.s_Score
) a1
where a1.名次=3)
and
(select max(s_Score) from Score where c_id='03')
) c;
+------+--------+------------+-------+--------+---------+
| s_id | s_name | s_birth | s_sex | c_name | s_Score |
+------+--------+------------+-------+--------+---------+
| 01 | 赵雷 | 1990-01-01 | 男 | 语文 | 80 |
| 02 | 钱电 | 1990-12-21 | 男 | 语文 | 70 |
| 03 | 孙风 | 1990-05-20 | 男 | 语文 | 80 |
| 05 | 周梅 | 1991-12-01 | 女 | 语文 | 76 |
| 01 | 赵雷 | 1990-01-01 | 男 | 数学 | 90 |
| 05 | 周梅 | 1991-12-01 | 女 | 数学 | 87 |
| 07 | 郑竹 | 1989-07-01 | 女 | 数学 | 89 |
| 01 | 赵雷 | 1990-01-01 | 男 | 英语 | 99 |
| 02 | 钱电 | 1990-12-21 | 男 | 英语 | 80 |
| 03 | 孙风 | 1990-05-20 | 男 | 英语 | 80 |
| 07 | 郑竹 | 1989-07-01 | 女 | 英语 | 98 |
+------+--------+------------+-------+--------+---------+
# 26、查询每门课程被选修的学生数
select c.c_id,c.c_name,count(1) from Course c
left join Score sc on sc.c_id=c.c_id
inner join Student st on st.s_id=c.c_id
group by st.s_id;
或
select c.c_id, c.c_name, count(s.s_id) '选修人数'
from Course c
left join Score s on c.c_id=s.c_id
group by c.c_id, c.c_name;
+------+--------+----------+
| c_id | c_name | 选修人数 |
+------+--------+----------+
| 01 | 语文 | 6 |
| 02 | 数学 | 6 |
| 03 | 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 st.s_id,st.s_name from Student st
left join Score sc on sc.s_id=st.s_id
inner join Course c on c.c_id=sc.c_id
group by st.s_id having count(1)=2;
或
select st.s_id, st.s_name
from Student st
left join Score s on st.s_id=s.s_id
group by st.s_id, st.s_name
having count(s.c_id)=2;
+------+--------+
| s_id | s_name |
+------+--------+
| 05 | 周梅 |
| 06 | 吴兰 |
| 07 | 郑竹 |
+------+--------+
# 28、查询男生、女生人数
select st.s_sex,count(1) from Student st group by st.s_sex;
+-------+----------+
| s_sex | count(1) |
+-------+----------+
| 男 | 4 |
| 女 | 4 |
+-------+----------+
# 29、查询名字中含有"风"字的学生信息
select st.* from Student st where st.s_name like "%风%";
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 03 | 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 st.*,count(1) from Student st group by st.s_name,st.s_sex having count(1)>1;
Empty set (0.00 sec)
注意5.7 以后的版本要修改配置文件：
如果my.cnf中有sql_mode配置，则将ONLY_FULL_GROUP_BY去掉。
如果没有，则将下面内容放到相应位置
[mysqld]
sql_mode=STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
发现从 MySQL 5.7.5 开始，默认 SQL 模式包括 ONLY_FULL_GROUP_BY。
（在 5.7.5 之前，MySQL 不检测函数依赖，并且默认不启用 ONLY_FULL_GROUP_BY。）
# 31、查询1990年出生的学生名单
select st.* from Student st where st.s_birth like "1990%";
或
select * from Student where year(s_birth) = '1990';
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
| 08 | 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(sc.s_Score) from Course c
inner join Score sc on sc.c_id=c.c_id
group by c.c_id, c.c_name order by avg(sc.s_Score) desc,c.c_id asc;
+------+--------+-----------------+
| c_id | c_name | avg(sc.s_Score) |
+------+--------+-----------------+
| 02 | 数学 | 72.6667 |
| 03 | 英语 | 68.5000 |
| 01 | 语文 | 64.5000 |
+------+--------+-----------------+
# 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 st.s_id,st.s_name,avg(sc.s_Score) from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id having avg(sc.s_Score)>=85;
+------+--------+-----------------+
| s_id | s_name | avg(sc.s_Score) |
+------+--------+-----------------+
| 01 | 赵雷 | 89.6667 |
| 07 | 郑竹 | 93.5000 |
+------+--------+-----------------+
# 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 st.s_name,sc.s_Score from Student st
inner join Score sc on sc.s_id=st.s_id and sc.s_Score<60
inner join Course c on c.c_id=sc.c_id and c.c_name ="数学" ;
或
select st.s_name, s.s_Score
from Student st
left join Score s on st.s_id=s.s_id
left join Course c on c.c_id=s.c_id
where c.c_name='数学' and s.s_Score<60;
+--------+---------+
| s_name | s_Score |
+--------+---------+
| 李云 | 30 |
+--------+---------+
# 35、查询所有学生的课程及分数情况；
select st.s_id,st.s_name,c.c_name,sc.s_Score from Student st
left join Score sc on sc.s_id=st.s_id
left join Course c on c.c_id =sc.c_id
order by st.s_id,c.c_name;
+------+--------+--------+---------+
| s_id | s_name | c_name | s_Score |
+------+--------+--------+---------+
| 01 | 赵雷 | 数学 | 90 |
| 01 | 赵雷 | 英语 | 99 |
| 01 | 赵雷 | 语文 | 80 |
| 02 | 钱电 | 数学 | 60 |
| 02 | 钱电 | 英语 | 80 |
| 02 | 钱电 | 语文 | 70 |
| 03 | 孙风 | 数学 | 80 |
| 03 | 孙风 | 英语 | 80 |
| 03 | 孙风 | 语文 | 80 |
| 04 | 李云 | 数学 | 30 |
| 04 | 李云 | 英语 | 20 |
| 04 | 李云 | 语文 | 50 |
| 05 | 周梅 | 数学 | 87 |
| 05 | 周梅 | 语文 | 76 |
| 06 | 吴兰 | 英语 | 34 |
| 06 | 吴兰 | 语文 | 31 |
| 07 | 郑竹 | 数学 | 89 |
| 07 | 郑竹 | 英语 | 98 |
| 08 | 王菊 | NULL | NULL |
+------+--------+--------+---------+
# 36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数
select st2.s_id,st2.s_name,c2.c_name,sc2.s_Score from Student st2
left join Score sc2 on sc2.s_id=st2.s_id
left join Course c2 on c2.c_id=sc2.c_id
where st2.s_id in(
select st.s_id from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id having min(sc.s_Score)>70)
order by s_id;
+------+--------+--------+---------+
| s_id | s_name | c_name | s_Score |
+------+--------+--------+---------+
| 01 | 赵雷 | 语文 | 80 |
| 01 | 赵雷 | 数学 | 90 |
| 01 | 赵雷 | 英语 | 99 |
| 03 | 孙风 | 语文 | 80 |
| 03 | 孙风 | 数学 | 80 |
| 03 | 孙风 | 英语 | 80 |
| 05 | 周梅 | 语文 | 76 |
| 05 | 周梅 | 数学 | 87 |
| 07 | 郑竹 | 数学 | 89 |
| 07 | 郑竹 | 英语 | 98 |
+------+--------+--------+---------+
# 37、查询不及格的课程
select st.s_id,c.c_name,st.s_name,sc.s_Score from Student st
inner join Score sc on sc.s_id=st.s_id and sc.s_Score<60
inner join Course c on c.c_id=sc.c_id ;
或
select st.s_id, st.s_name, c.c_name, s.s_Score from Student st
left join Score s on s.s_id=st.s_id
left join Course c on c.c_id=s.c_id
where s.s_Score<60;
+------+--------+--------+---------+
| s_id | c_name | s_name | s_Score |
+------+--------+--------+---------+
| 04 | 语文 | 李云 | 50 |
| 04 | 数学 | 李云 | 30 |
| 04 | 英语 | 李云 | 20 |
| 06 | 语文 | 吴兰 | 31 |
| 06 | 英语 | 吴兰 | 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 st.s_id,st.s_name,sc.s_Score from Student st
inner join Score sc on sc.s_id=st.s_id and sc.c_id="01" and sc.s_Score>=80;
+------+--------+---------+
| s_id | s_name | s_Score |
+------+--------+---------+
| 01 | 赵雷 | 80 |
| 03 | 孙风 | 80 |
+------+--------+---------+
# 39、求每门课程的学生人数
select c.c_id,c.c_name,count(1) from Course c
inner join Score sc on sc.c_id=c.c_id
group by c.c_id;
或
select c.c_id, c.c_name, count(st.s_id)
from Course c
left join Score s on c.c_id=s.c_id
left join Student st on s.s_id=st.s_id
group by c.c_id, c.c_name;
+------+--------+----------------+
| c_id | c_name | count(st.s_id) |
+------+--------+----------------+
| 01 | 语文 | 6 |
| 02 | 数学 | 6 |
| 03 | 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 st.*,c.c_name,sc.s_Score,t.t_name from Student st
inner join Score sc on sc.s_id=st.s_id
inner join Course c on c.c_id=sc.c_id
inner join Teacher t on t.t_id=c.t_id and t.t_name="张三"
order by sc.s_Score desc
limit 0,1;
或
select st.*, s.s_Score, t.t_name, c.c_name
from Student st
left join Score s on st.s_id=s.s_id
left join Course c on s.c_id=c.c_id
left join Teacher t on c.t_id=t.t_id
where t.t_name='张三'
and s.s_Score = (
select distinct max(s2.s_Score)
from Score s2 left join Course c2 on s2.c_id=c2.c_id
left join Teacher t2 on c2.t_id=t2.t_id
where t2.t_name='张三'
);
+------+--------+------------+-------+---------+--------+--------+
| s_id | s_name | s_birth | s_sex | s_Score | t_name | c_name |
+------+--------+------------+-------+---------+--------+--------+
| 01 | 赵雷 | 1990-01-01 | 男 | 90 | 张三 | 数学 |
+------+--------+------------+-------+---------+--------+--------+
# *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 st.s_id,st.s_name,sc.c_id,sc.s_Score,c.c_name from Student st
left join Score sc on sc.s_id=st.s_id
left join Course c on c.c_id=sc.c_id
where (
select count(1) from Student st2
left join Score sc2 on sc2.s_id=st2.s_id
left join Course c2 on c2.c_id=sc2.c_id
where sc.s_Score=sc2.s_Score and c.c_id!=c2.c_id
)>1;
+------+--------+------+---------+--------+
| s_id | s_name | c_id | s_Score | c_name |
+------+--------+------+---------+--------+
| 01 | 赵雷 | 01 | 80 | 语文 |
| 03 | 孙风 | 01 | 80 | 语文 |
| 03 | 孙风 | 02 | 80 | 数学 |
| 02 | 钱电 | 03 | 80 | 英语 |
| 03 | 孙风 | 03 | 80 | 英语 |
+------+--------+------+---------+--------+
5 rows in set (0.00 sec)
# 42、查询每门功成绩最好的前两名
select a.* from (select st.s_id,st.s_name,c.c_name,sc.s_Score from Student st
left join Score sc on sc.s_id=st.s_id
inner join Course c on c.c_id=sc.c_id and c.c_id="01"
order by sc.s_Score desc limit 0,2) a
union all
select b.* from (select st.s_id,st.s_name,c.c_name,sc.s_Score from Student st
left join Score sc on sc.s_id=st.s_id
inner join Course c on c.c_id=sc.c_id and c.c_id="02"
order by sc.s_Score desc limit 0,2) b
union all
select c.* from (select st.s_id,st.s_name,c.c_name,sc.s_Score from Student st
left join Score sc on sc.s_id=st.s_id
inner join Course c on c.c_id=sc.c_id and c.c_id="03"
order by sc.s_Score desc limit 0,2) c;
+------+--------+--------+---------+
| s_id | s_name | c_name | s_Score |
+------+--------+--------+---------+
| 01 | 赵雷 | 语文 | 80 |
| 03 | 孙风 | 语文 | 80 |
| 01 | 赵雷 | 数学 | 90 |
| 07 | 郑竹 | 数学 | 89 |
| 01 | 赵雷 | 英语 | 99 |
| 07 | 郑竹 | 英语 | 98 |
+------+--------+--------+---------+
-- 借鉴(更准确,漂亮):
select a.s_id,a.c_id,a.s_Score from Score a
where (select COUNT(1) from Score b where b.c_id=a.c_id and b.s_Score>=a.s_Score)<=2 order by a.c_id;
# 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 sc.c_id,count(1) from Score sc
left join Course c on c.c_id=sc.c_id
group by c.c_id having count(1)>5
order by count(1) desc,sc.c_id asc;
或
select c.c_id, count(s.s_id)
from Course c left join Score s on c.c_id=s.c_id
group by c.c_id
having count(s.s_id)>5
order by count(s.s_id) desc, c.c_id;
+------+---------------+
| c_id | count(s.s_id) |
+------+---------------+
| 01 | 6 |
| 02 | 6 |
| 03 | 6 |
+------+---------------+
# 44、检索至少选修两门课程的学生学号
select st.s_id from Student st
left join Score sc on sc.s_id=st.s_id
group by st.s_id having count(1)>=2;
+------+
| s_id |
+------+
| 01 |
| 02 |
| 03 |
| 04 |
| 05 |
| 06 |
| 07 |
+------+
# 45、查询选修了全部课程的学生信息
select st.*
from Student st left join Score s on st.s_id=s.s_id
group by st.s_id
having count(s.c_id)=(select count(*) from Course);
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 02 | 钱电 | 1990-12-21 | 男 |
| 03 | 孙风 | 1990-05-20 | 男 |
| 04 | 李云 | 1990-08-06 | 男 |
+------+--------+------------+-------+
# *46、查询各学生的年龄(实岁)
select st.*,timestampdiff(year,st.s_birth,now()) from Student st;
+------+--------+------------+-------+--------------------------------------+
| s_id | s_name | s_birth | s_sex | timestampdiff(year,st.s_birth,now()) |
+------+--------+------------+-------+--------------------------------------+
| 01 | 赵雷 | 1990-01-01 | 男 | 33 |
| 02 | 钱电 | 1990-12-21 | 男 | 32 |
| 03 | 孙风 | 1990-05-20 | 男 | 33 |
| 04 | 李云 | 1990-08-06 | 男 | 33 |
| 05 | 周梅 | 1991-12-01 | 女 | 32 |
| 06 | 吴兰 | 1992-03-01 | 女 | 31 |
| 07 | 郑竹 | 1989-07-01 | 女 | 34 |
| 08 | 王菊 | 1990-01-20 | 女 | 33 |
+------+--------+------------+-------+--------------------------------------+
8 rows in set (0.01 sec)
# 47、查询本周过生日的学生
select st.* from Student st
where week(now())=week(date_format(st.s_birth,'%Y%m%d'));
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 02 | 钱电 | 1990-12-21 | 男 |
+------+--------+------------+-------+
1 row in set (0.01 sec)
# 48、查询下周过生日的学生(还要排除闰年情况)
select st.* from Student st
where week(now())+1=week(date_format(st.s_birth,'%Y%m%d'));
Empty set (0.00 sec)
# 49、查询本月过生日的学生
select st.* from Student st
where month(now())=month(date_format(st.s_birth,'%Y%m%d'));
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 02 | 钱电 | 1990-12-21 | 男 |
| 05 | 周梅 | 1991-12-01 | 女 |
+------+--------+------------+-------+
2 rows in set (0.01 sec)
# *50、查询下月过生日的学生
# 注意:当 当前月为12时,用month(now())+1为13而不是1,可用timestampadd()函数或mod取模
select st.* from Student st
where month(timestampadd(month,1,now()))=month(date_format(st.s_birth,'%Y%m%d'));
-- 或
select st.* from Student st where (month(now()) + 1) mod 12 = month(date_format(st.s_birth,'%Y%m%d'))
+------+--------+------------+-------+
| s_id | s_name | s_birth | s_sex |
+------+--------+------------+-------+
| 01 | 赵雷 | 1990-01-01 | 男 |
| 08 | 王菊 | 1990-01-20 | 女 |
+------+--------+------------+-------+
2 rows in set (0.00 sec)
二、综合演练：
Sakila 是一个在线 DVD 出租商店数据库，
为各种 MySQL 文档、书籍、教程、文章、示例等提供了一个标准数据库模式；同时，
它还可以用于演示 MySQL 的其他功能特性，例如视图、存储过程和触发器。
Sakila 数据库的模式结构如下图所示：
Sakila 数据库提供了以下数据表：
actor， 演员信息表。通过 film_actor 表和 film 表进行关联。
film， 电影信息表。film 引用了 language 表，同时被 film_category、film_actor 以及 inventory 表引用。
film_actor， 电影演员表。film 表和 actor 表之间的多对多关系。
film_category， 电影分类表。film 表和 category 表之间的多对多关系。
category， 分类表。通过 film_category 表和 film 表进行关联。
inventory， 电影库存表。每部电影在不同商店里的库存，被 rental 表引用。
film_text， 电影描述表。包含了film表中的 film_id、title 以及description三个字段，通过film表触发器进行数据同步。
language， 语言信息表。language 表被 film 表引用。
address， 地址信息表。其中主键字段 address_id 是 customer、staff 以及 store 表上的外键引用字段，
同时引用了 city 表。
city， 城市信息表。引用了 country 表，同时被 address 表引用。
country， 国家信息表。country 表被 city 表引用。
customer， 客户信息表。引用了 address 和 store 表，同时被 payment 和 rental 表引用。
payment， 付款信息表。引用了 customer、staff 以及 rental 表。
rental， 租赁信息表，每个 DVD 每次被租赁的信息。引用了 inventory、customer 以及 staff 表，
同时被 payment 表引用。
staff， 员工信息表。引用了 store 和 address 表，同时被 rental、payment 以及 store 表引用。
store， 商店信息表，引用了 staff 和 address 表，同时被 staff、customer 以及 inventory 表引用。
Sakila 数据库提供了以下视图：
actor_info， 包含了所有的演员，以及他们演出过的电影。
customer_list， 客户和地址信息列表。
film_list， 电影信息和参与的演员。
nicer_but_slower_film_list， 电影信息和参与的演员，演员的姓名调整为首字母大写。
sales_by_film_category， 按照不同电影分类统计的销售金额，同一个电影可能被分为多个类别。
sales_by_store，按照商店统计的销售金额。
staff_list， 员工列表，包括地址和所属的商店。
Sakila 数据库提供了以下存储过程和函数：
film_in_stock， 存储过程，获取指定电影在指定商店内未出租的 DVD。
film_not_in_stock， 存储过程，获取指定电影在指定商店内已出租未归还的 DVD。
rewards_report， 存储过程，获取上个月的最佳客户列表。
get_customer_balance， 存储函数，返回指定客户在某个日期之前的欠款。
inventory_held_by_customer，存储函数，返回正在租赁某个 DVD 的客户。
inventory_in_stock， 存储函数，返回某个 DVD 是否可出租。TRUE 表示可以出租，FALSE 表示已出租未归还。
Sakila 数据库包含了以下触发器：
customer_create_date， 插入数据时将 customer 表的 create_date 字段设置为当前日期和时间。
payment_date， 插入数据时将 payment 表的 payment_date 字段设置为当前日期和时间。
rental_date， 插入数据时将 rental 表的 rental_date 字段设置为当前日期和时间。
ins_film， 将 film 表上插入的相关数据复制一份到 film_text 表。
upd_film， 将 film 表上更新的相关数据同步到 film_text 表。
del_film， 删除 film 表数据时同步删除 film_text 表上的相关数据。
Sakila 数据库的创建脚本可以点此下载，然后运行以下命令创建数据库并初始化数据：
shell> mysql -t < sakila-schema.sql;
shell> mysql -t < sakila-data.sql;
创建成功之后，可以执行以下语句进行验证：
mysql> USE sakila;
Database changed
mysql> SHOW FULL TABLES;
+----------------------------+------------+
| Tables_in_sakila | Table_type |
+----------------------------+------------+
| actor | BASE TABLE |
| actor_info | VIEW |
| address | BASE TABLE |
| category | BASE TABLE |
| city | BASE TABLE |
| country | BASE TABLE |
| customer | BASE TABLE |
| customer_list | VIEW |
| film | BASE TABLE |
| film_actor | BASE TABLE |
| film_category | BASE TABLE |
| film_list | VIEW |
| film_text | BASE TABLE |
| inventory | BASE TABLE |
| language | BASE TABLE |
| nicer_but_slower_film_list | VIEW |
| payment | BASE TABLE |
| rental | BASE TABLE |
| sales_by_film_category | VIEW |
| sales_by_store | VIEW |
| staff | BASE TABLE |
| staff_list | VIEW |
| store | BASE TABLE |
+----------------------------+------------+
23 rows in set (0.01 sec)
mysql> SELECT COUNT(*) FROM film;
+----------+
| COUNT(*) |
+----------+
| 1000 |
+----------+
1 row in set (0.00 sec)
mysql> SELECT COUNT(*) FROM film_text;
+----------+
| COUNT(*) |
+----------+
| 1000 |
+----------+
1 row in set (0.00 sec)
关于 Sakila 数据库的详细介绍和使用可以查看官方文档。https://dev.mysql.com/doc/sakila/en/
以上资料来源：https://www.cnblogs.com/dersome/p/14902838.html
![[C#]OpenCvSharp结合yolov8-face实现L2CS-Net眼睛注视方向估计或者人脸朝向估计](https://img-blog.csdnimg.cn/direct/909af88688144d84b280121f3fd6305d.jpeg)
