请编写 SQL 语句，查询 teachers 表中，各个国家所有教师的平均年龄大于所有国家教师的平均年龄的教师信息。

Question

表定义: teachers (教师表)

列名 类型 注释
id int unsigned 主键
name varchar 讲师姓名
email varchar 讲师邮箱
age int 讲师年龄
country varchar 讲师国籍

Answer 1

一步一步的来
1、所有国家教师的平均年龄
select avg(age) from teachers

2、大于平均年龄的国家
select country from teachers group by country having avg(agr)>(
select avg(age) from teachers
)

3、这些国家的教师
select * from teachers where country in (
select country from teachers group by country having avg(agr)>(
select avg(age) from teachers
)
)