多表查询

SELECT employee_id,department_name
from employees e,departments d
WHERE e.department_id=d.department_id;

SELECT * FROM employees;

SELECT employee_id,department_name
from employees e INNER JOIN departments d
on e.department_id=d.department_id;

SELECT employee_id,department_name,city
from employees e JOIN departments d
JOIN locations l
on e.department_id=d.department_id and
d.location_id=l.location_id;

SELECT employee_id,department_name
from employees e left JOIN departments d
on e.department_id=d.department_id;

SELECT employee_id,department_name
FROM employees e RIGHT JOIN departments d
on e.department_id=d.department_id;