SQL练习54：查找排除当前最大、最小salary之后的员工的平均工资avg_salary

题目链接：牛客网

题目描述
查找排除最大、最小salary之后的当前(to_date = '9999-01-01' )员工的平均工资avg_salary。

CREATE TABLE `salaries` ( `emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`from_date`));
如：
INSERT INTO salaries VALUES(10001,85097,'2001-06-22','2002-06-22');
INSERT INTO salaries VALUES(10001,88958,'2002-06-22','9999-01-01');
INSERT INTO salaries VALUES(10002,72527,'2001-08-02','9999-01-01');
INSERT INTO salaries VALUES(10003,43699,'2000-12-01','2001-12-01');
INSERT INTO salaries VALUES(10003,43311,'2001-12-01','9999-01-01');
INSERT INTO salaries VALUES(10004,70698,'2000-11-27','2001-11-27');
INSERT INTO salaries VALUES(10004,74057,'2001-11-27','9999-01-01');

输出格式:

avg_salary
73292

解法
解题思想就是想办法去除最大工资和最小工资，这里使用子查询的方式，要注意一点的是题中少了一个条件，就是要限定to_date = '9999-01-01'，表示获取当前数据。

SELECT AVG(salary) avg_salary
FROM salaries
WHERE to_date = '9999-01-01'
AND salary NOT IN (SELECT MAX(salary)
                  FROM salaries
                  WHERE to_date = '9999-01-01')
AND salary NOT IN (SELECT MIN(salary)
                  FROM salaries
                  WHERE to_date = '9999-01-01')