一、 导入hellodb.sql生成数据库

首先导入hellodb.sql生成数据库
MariaDB [(none)]> mysql -uroot -pmeng < hellodb_innodb.sql
切换数据库
MariaDB [(none)]> use hellodb

1、在students表中，查询年龄大于25岁，且为男性的同学的名字和年龄

MariaDB [hellodb]> select name 姓名,age 年龄,gender 性别 from students where age >25;

2 、以ClassID为分组依据，显示每组的平均年龄

MariaDB [hellodb]> select classid,avg(age) from students where classid is not null group by classid;

或者执行：

MariaDB [hellodb]> select classid,avg(age) from students group by classid having classid is not null;

3、显示第2题中平均年龄大于30的分组及平均年龄

MariaDB [hellodb]> select classid,avg(age) from students group by classid having classid is not null and avg(age) > 30;

4、显示以L开头的名字的同学的信息

MariaDB [hellodb]> select * from students where name rlike '^l';