N46030-段鹏-第十三周作业

1、如何将 hellodb_innodb.sql导入到数据库中

 mysql < helldb.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  gender='M' and age > 25;

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 where classid is not null group by classid;

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) from (select classid,age from students where gender='M' and age > 25) as f_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 rlike '^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 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(*) 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,avg(age) from students group by classid having avg(age) > 25;