【396天】我爱刷题系列155（2018.03.08）

@(跃迁之路)专栏

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SQL习题050

题目描述
查找排除当前最大、最小salary之后的员工的平均工资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));

输出格式:
avg_salary
69462.5555555556

本题逻辑有问题，在挑选当前最大、最小salary时没加 to_date = '9999-01-01' 作条件限制，导致挑选出来的是全表最大、最小salary，然后对除去这两个salary再作条件限制 to_date = '9999-01-01' ，求平均薪水，此时求出的平均薪水与题目逻辑要求的不同。

SELECT AVG(salary) AS avg_salary FROM salaries 
WHERE to_date = '9999-01-01' 
AND salary NOT IN (SELECT MAX(salary) FROM salaries)
AND salary NOT IN (SELECT MIN(salary) FROM salaries)
正确的逻辑应如下所示，但在本题OJ系统中通不过：

SELECT AVG(salary) AS 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')