[打卡]赵博玲内外连接

SELECT e.employee_id,d.department_name 
from employees e,departments d 
WHERE e.department_id=d.department_id;
SELECT employee_id,department_name
from employees e JOIN departments d 
ON e.department_id=d.department_id;
SELECT employee_id,department_name
from employees e inner JOIN departments d 
ON e.department_id=d.department_id;
#SQL99内连接
SELECT employee_id,department_name,city
from employees e 
JOIN departments d ON e.department_id=d.department_id
JOIN locations l on d.location_id=l.location_id;
-- SQL99外连接
#左外连接outer可省略
SELECT employee_id,department_name
from employees e LEFT OUTER JOIN
departments d on e.department_id=d.department_id;
SELECT employee_id,department_name
from employees e LEFT  JOIN
departments d on e.department_id=d.department_id;
#右外连接
SELECT employee_id,department_name
from employees e RIGHT  JOIN
departments d on e.department_id=d.department_id;