标题

SELECT employee_id,department_name
FROM employees,departments
WHERE employees.department_id=departments.department_id;


SELECT employee_id,department_name
FROM employees,departments
WHERE employees.department_id=departments.department_id(+);



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;

#左外连接
SELECT employee_id,department_name
FROM employees e LEFT OUTER JOIN
departments d ON e.department_id=d.department_id;
# OUTER 可以省略

#右外连接
SELECT employee_id,department_name
FROM employees e RIGHT OUTER JOIN
departments d
ON e.department_id=d.department_id;