多表查询-----练习一

分类1：等值连接 vs 非等值连接

分类2：自连接 vs 非自连接

分类3：内连接 vs 外连接

【题目】
# 1.显示所有员工的姓名，部门号和部门名称。
# 2.查询90号部门员工的job_id和90号部门的location_id
# 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
# 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
employees Emp# manager Mgr#
kochhar 101 king 100
# 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

# 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 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 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

SELECT e.last_name,d.department_name,d.location_id,l.city
FROM employees e LEFT JOIN departments d 
ON    e.department_id=d.department_id
LEFT JOIN locations l
ON d.location_id=l.location_id
WHERE commission_pct IS NOT NULL;

# 4.选择city在Toronto工作的员工的 last_name , job_id , department_id , department_name

SELECT e.last_name , e.job_id , d.department_id , d.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
WHERE l.city='Toronto';

# 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’

SELECT d.department_name,l.street_address,e.last_name,e.job_id,e.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';

# 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
#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 JOIN employees mgr
ON emp.manager_id = mgr.employee_id;

# 7.查询哪些部门没有员工

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

# 8. 查询哪个城市没有部门

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;

# 9. 查询部门名为 Sales 或 IT 的员工信息
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');