# 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 e.job_id,d.location_id
FROM employees e JOIN departments d 
ON e.`department_id` = d.`department_id`
WHERE d.`department_id` = 90

DESC departments;
# 3.选择所有有奖金的员工的 last_name , department_name , location_id , city
SELECT e.last_name,e.`commission_pct`,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 e.`commission_pct` IS NOT NULL;#也应该是35条记录

SELECT *
FROM employees
WHERE commission_pct IS NOT NULL; #35条
# 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';

#sq192语法：
SELECT e.last_name,e.job_id,d.department_id,d.department_name
FROM employees e,departments d,locations l
WHERE e.`department_id` = d.`department_id`
AND d.`location_id` = l.`location_id`
AND 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 departments d LEFT JOIN employees e
ON e.`department_id` = d.`department_id`
LEFT JOIN locations l
ON d.`location_id` = l.`location_id`
WHERE d.`department_name` = 'Executive';

DESC departments;

DESC locations;
# 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 "employess",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 d.`department_id` = e.`department_id`
WHERE e.`department_id` IS NULL;
#本题也可使用子查询：暂时不讲解

# 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;

SELECT department_id
FROM departments
WHERE department_id IN (1000,1100,1200,1300,1600);

# 9. 查询部门名为 Sales 或 IT 的员工信息

SELECT e.employee_id,e.last_name,e.department_id
FROM employees e JOIN departments d
ON e.`department_id` =d.`department_id`
WHERE d.`department_name` IN ('Sales','IT');