博客第18周

1、如何将 hellodb_innodb.sql导入到数据库中

create database hellodb;

use hellodb;

source /root/hellodb_innodb.sql;

2、在学生表中，查询年龄大于25岁，且为男性的同学的名字和年龄

 select name,age from students where age > 25 and gender='M';

3、在学生表中，以ClassID为分组依据，查询显示每组的平均年龄

 select ClassID,avg(age) from students ;

4、显示第2题中平均年龄大于30的分组及平均年龄

select ClassID,avg(age) as a from (select  ClassID,age from students where age > 25 and gender='M')as classID_age group by ClassID having avg(age)>30;

5、显示以L开头的名字的同学的信息

 select * from students where name like 'L%';

6、显示老师ID非空的同学的相关信息

 select * from students where TeacherID is not NULL;

7、students表中，查询以年龄排序后的数据，并且显示年龄最大的前10位同学的信息

 select * from students order by age desc limit 10;

8、students表中，查询年龄大于等于20岁，小于等于25岁的同学的信息

 select * from students where age between 20 and 25;

9、以ClassID分组，显示每班的同学的人数

 select ClassID,count(ClassID) from students group by ClassID;

10、以ClassID分组，显示其平均年龄大于25的班级

select ClassID from students group by ClassID having avg(age)>25;