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select * from employees;
select * from departments;
select department_id,avg(salary) from employees group by department_id;

 

用子查詢解

**************

select d.employee_id,d.first_name,d.last_name,d.department_id from employees d
where salary>(select avg(salary) from employees e where e.department_id=d.department_id)
order by d.employee_id;

**************

其中where e.department_id=d.department_id 有group by的意義

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