mysql连接图.png
SELECT first_name,last_name,department_name
FROM employees e
LEFT JOIN departments d ON d.department_id=e.department_id
WHERE d.department_name IN('Sal','IT')
SELECT first_name,last_name,department_name
FROM employees e
LEFT JOIN departments d ON d.department_id=e.department_id
WHERE d.department_name IN('Sal','IT')