SQL增查

建完库与建完表后后:

1.分别查询student表和score表的所有记录

 student表：

score表:

2.查询student表的第2条到5条记录

SELECT * FROM student LIMIT 1,4;

3.从student表中查询计算机系和英语系的学生的信息

SELECT * FROM student
    -> WHERE department IN ('计算机系', '英语系');

4.从student表中查询年龄小于22岁的学生信息

select * from student
    -> where 2025 - birth < 22 ;

5.从student表中查询每个院系有多少人

select department, count(*) as student_count
    -> from student
    -> group by department;

6.从score表中查询每个科目的最高分

select c_name,max(grade) as max_grade
    -> from score
    -> group by c_name;

7.查询李广昌的考试科目(c name)和考试成绩(grade)

select s.c_name , s.grade
    -> from student st
    -> join score s on st.id = s.stu_id
    -> where st.name = '李广昌';

8.用连接的方式查询所有学生的信息和考试信息

select st.*,s.c_name,s.grade
    -> from student st
    -> left join score s on st.id = s.stu_id;

9.计算每个学生的总成绩

select stu_id,sum(grade) as total_grade
    -> from score
    -> group by stu_id;

10.计算每个考试科目的平均成绩

select c_name,avg(grade) as avg_grade
    -> from score
    -> group by c_name;

11.查询计算机成绩低于95的学生信息

select st.*
    -> from student st
    -> join score s on st.id = s.stu_id
    -> where s.c_name = '计算机' AND s.grade < 95
    -> ;

12,将计算机考试成绩按丛高到低进行排序

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

13.从student表和score表中查询出学生的学号，然后合并查询结果

select id as student_id
    -> from  student
    -> union
    -> select stu_id from score;

14.查询姓张或者姓王的同学的姓名、院系和考试科目及成绩

select st.name , st.department , s.c_name , s.grade
    -> from student st
    -> left join score s on st.id = s.stu_id
    -> where st.name like '张%' or st.name like '王%';

15.查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩

 select st.name , 2025 - st.birth as age ,st.department , s.c_name , s.grade
    -> from student st
    -> left join score s on st.id = s.stu_id
    -> where st.address like '%湖南省%';