select employee_id, last_name, department_id
from employees e
order by department_id;//这个好理解
这个就是用这个employees对应的部门号来排序select employee_id, last_name, department_id
from employees e
order by (select department_name
from departments d
where e.department_id = d.department_id)
这个就是用这个employees对应的部门名来排序order by后还可以跟decode,自定义的排序函数
from employees e
order by department_id;//这个好理解
这个就是用这个employees对应的部门号来排序select employee_id, last_name, department_id
from employees e
order by (select department_name
from departments d
where e.department_id = d.department_id)
这个就是用这个employees对应的部门名来排序order by后还可以跟decode,自定义的排序函数
这句话是什么意思啊select employee_id, last_name, department_id
from employees e
join departments d using(department_id)
order by d.department_name;
使用部门名称来排序。我比较两个结果,前者比后者的结果众多了一个department_id为null的row
select e.employee_id, e.last_name, e.department_id,d.department_name
from employees e,departments d
where e.department_id = d.department_name (+)
order by d.department_name;
的意思。