1.显示所有员工的姓名，部门号和部门名称
SELECT last_name, e.department_id, department_name
FROM employees e
LEFT OUTER JOIN departments d
ON e.department_id = d.department_id;
2.查询90号部门员工的job_id和90号部门的location_id
SELECT job_id, location_id
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND e.department_id = 90;
或
SELECT job_id, location_id
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
WHERE e.department_id = 90;
3.选择所有有奖金的员工的 last_name , department_name , location_id ,
city
4.选择city在Toronto工作的员工的 last_name , job_id , department_id ,
department_name
或
5．查询员工所在的部门名称、部门地址、姓名、工作、工资，其中员工所
在部门的部门名称为’Executive’

6. 选择指定员工的姓名，员工号，以及他的管理者的姓名和员工号，结果
   类似于下面的格式
   SELECT last_name , department_name , d.location_id , city
   FROM employees e
   LEFT OUTER JOIN departments d
   ON e.department_id = d.department_id
   LEFT OUTER JOIN locations l
   ON d.location_id = l.location_id
   WHERE commission_pct IS NOT NULL;
   SELECT last_name , job_id , e.department_id , department_name
   FROM employees e, departments d, locations l
   WHERE e.department_id = d.department_id
   AND d.location_id = l.location_id
   AND city = 'Toronto';
   SELECT last_name , job_id , e.department_id , department_name
   FROM employees e
   JOIN departments d
   ON e.department_id = d.department_id
   JOIN locations l
   ON l.location_id = d.location_id
   WHERE l.city = 'Toronto';
   SELECT department_name, street_address, last_name, job_id, salary
   FROM employees e JOIN departments d
   ON e.department_id = d.department_id
   JOIN locations l
   ON d.location_id = l.location_id
   WHERE department_name = 'Executive'
   employees Emp# manager Mgr#
   kochhar 101 king 100
   SELECT emp.last_name employees, emp.employee_id "Emp#", mgr.last_name manager,
   mgr.employee_id "Mgr#"
   FROM employees emp
   LEFT OUTER JOIN employees mgr
   ON emp.manager_id = mgr.employee_id;
7. 查询哪些部门没有员工
8. 查询哪个城市没有部门
9. 查询部门名为 Sales 或 IT 的员工信息
   多表查询-2

方式1：

SELECT d.department_id
FROM departments d LEFT JOIN employees e
ON e.department_id = d.department_id
WHERE e.department_id IS NULL

方式2：

SELECT department_id
FROM departments d
WHERE NOT EXISTS (
SELECT *
FROM employees e
WHERE e.department_id = d.department_id
)
SELECT l.location_id,l.city
FROM locations l LEFT JOIN departments d
ON l.location_id = d.location_id
WHERE d.location_id IS NULL
SELECT employee_id,last_name,department_name
FROM employees e,departments d
WHERE e.department_id = d.department_id
AND d.department_name IN ('Sales','IT');