解决Mysql多行子查询的使用及空值问题

-- 多行子查询

-- IN
SELECT
	employee_id,
	manager_id,
	department_id 
FROM
	employees 
WHERE
	manager_id IN ( -- 在返回集合中查找有没有相同的manager_id在里面
	SELECT
		manager_id 
	FROM
		employees 
	WHERE
	employee_id IN ( 141, 147 ));
	
-- ANY
#题目：返回其它job_id中比job_id为'IT_PROG'部门任一工资低的员工的员工号、姓名、job_id 以及salary
	last_name,
	job_id,
	salary 
	job_id != 'IT_PROG' 
	AND salary < ANY ( -- 比任意一个小都可以
	SELECT salary FROM employees WHERE job_id = 'IT_PROG' );
-- ALL
#题目：返回其它job_id中比job_id为'IT_PROG'部门所有工资低的员工的员工号、姓名、job_id 以及salary
	AND salary < ALL ( -- 比所有的都小才可以

	-- 空值问题
SELECT
	last_name 
FROM
	employees 
WHERE
	employee_id NOT IN (
	SELECT -- 子查询中的结果有NULL
		manager_id 
	employees)

	-- 空值问题解决
SELECT
	last_name 
FROM
	employees 
WHERE
	employee_id NOT IN (
	SELECT
		manager_id 
	FROM
		employees 
	manager_id IS NOT NULL)