Oracle where语句中等号两边的是否可以互换?
with reporting_hierarchy
(employee_id, manager_id, reporting_level,first_name,last_name,salary, title)as
(select employee_id, manager_id, 0 reporting_level, first_name, last_name,salary, title from more_employees
union all
select e.employee_id, e.manager_id,r.reporting_level + 1 as reporting_level, e.first_name,e.last_name,e.salary, e.title
from reporting_hierarchy r, more_employees e
where r.employee_id=e.manager_id
)
search depth first by employee_id set order_by_employee_id
cycle title set same_title to 'Y' default 'N'
select employee_id, manager_id, lpad(' ',2*reporting_level)||first_name||' '||last_name as employee, salary, title, same_title
from reporting_hierarchy
order by order_by_employee_id;
在where句中,r.employee_id=e.manager_id和e.employee_id=r.manager_id 互换有什么区别?作用是什么?