Database multi-table query job

Database multi-table query job

Create a database

and insert data

mysql> insert into student values(901,'张老大','男',1985,'计算机系','北京市海淀区'),
    -> (902,'张老二','男',1986,'中文系','北京市昌平市'),
    -> (903,'张三','女',1990,'中文系','湖南省永州市'),                                           -> (904,'李四','男',1990,'英语系','辽宁省阜新市'),                                           -> (905,'王五','女',1991,'英语系','福建省厦门市'),
    -> (906,'王六','男',1988,'计算机系','湖南省衡阳市');

mysql> insert into score values(null,901,'计算机',98),
    -> (null,901,'英语',80),
    -> (null,902,'计算机',65),
    -> (null,902,'中文',88),
    -> (null,903,'中文',95),
    -> (null,904,'计算机',70),
    -> (null,904,'英语',92),
    -> (null,905,'英语',94),
    -> (null,906,'计算机',90),
    -> (null,906,'英语',85);

1. Query all records of the student table

mysql> select * from student;

2. Query the 2nd to 4th records of the student table

mysql> select * from student limit 1,3;

3. Query the student number (id), name
(name) and department (department) information of all students from the student table

mysql> select id as 学号,name as 姓名,department as 院系 from student;

4. Query the information of the students of the computer department and the English department from the student table

mysql> select * from student where department='计算机系' or department='英语系';

5. Query the information of students aged 18~22 from the student table

mysql> select *,year(curdate())-birth as age from student where year(curdate())-birth between 18 and 22;

6. Query how many people are in each department from the student table

mysql> select department as 院系,count(*) as 人数 from student group by department;

7. Query the highest score of each subject from the score table

mysql> select c_name as 科目,max(grade) as 最高分 from score group by c_name;

8. Query Li Si's test subjects (c_name) and test results (grade)

mysql> select name as 姓名,c_name as 科目,grade as 成绩 from student
    -> inner join score on student.id=score.stu_id
    -> where name='李四';

9. Query all student information and test information by connecting

mysql> select * from student iudent inner join score on student.id=score.stu_id;

10. Calculate the total grade of each student

mysql> select name as 姓名,sum(grade) as 总成绩 from student
    -> inner join score on student.id=score.stu_id
    -> group by name;

11. Calculate the average grade for each exam subject

mysql> select avg(grade) from score group by c_name;

12. Query the information of students whose computer scores are lower than 95

mysql> select * from student
    -> inner join (select stu_id,c_name,grade from score where grade<95 and c_name='计算机') as stu
    -> on student.id=stu.stu_id;

13. Query the information of students who take both computer and English exams

Obtain the student ID of the computer and English test at the same time

select * from score where c_name='英语') as sc2 where sc1.stu_id=sc2.stu_id

Get student information by ID

mysql> select * from student inner join (select sc1.stu_id from (select * from score where c_name='计算机') as sc1,(select * from score where c_name='英语') as sc2 where sc1.stu_id=sc2.stu_id) as sc on student.id=sc.stu_id;

14. Sort computer test scores from high to low

mysql> select * from score where c_name='计算机' order by grade desc;

15. Query the student ID number from the student table and score table, and then merge the query results

mysql> select student.id,score.stu_id from student inner join (select distinct stu_id from score) as score on student.id=score.stu_id;

16. Query the name, department, examination subjects and grades of students surnamed Zhang or Wang

mysql> select stu.name as 姓名, stu.department as 院系, score.c_name as 科目,score.grade as  成绩
    -> from score inner join
    -> (select * from student where name like '张%' or name like '王') as stu
    -> on score.stu_id=stu.id;

17. Query the names, ages, departments, examination subjects and grades of students from Hunan

mysql> select stu.name as 姓名,year(curdate())-stu.birth as age,stu.department as 院系,score.c_name as 科目,score.grade as 成绩
    -> from score
    -> inner join
    -> (select * from student where address like '%湖南%') as stu
    -> on score.stu_id=stu.id;