张博研——多表查询

SELECT employee_id,department_name from
employees,departments where employees.department_id=
departments.department_id;
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;

SELECT employee_id,department_name
FROM employees e JOIN departments d
ON e.department_id = d.department_id
JOIN locations l
ON 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;