MySQL查询问题：如何计算并筛选18-25岁的人员数据

错误原因 #

你写的SQL报错是因为WHERE子句里把函数名TIMESTAMPDIFF当成列名用了，数据库找不到这个列，所以抛出#1054错误。

正确的单条查询写法 #

不需要拆分多条查询，单条语句就能实现需求，下面是几种可行写法：

写法一：WHERE子句直接计算年龄 #

直接在WHERE里完整调用函数计算年龄，再做范围判断：

SELECT name, TIMESTAMPDIFF(YEAR, birthday, CURDATE()) AS age
FROM personnel
WHERE TIMESTAMPDIFF(YEAR, birthday, CURDATE()) BETWEEN 18 AND 25;

写法二：用HAVING过滤别名 #

MySQL的WHERE不能直接用SELECT里定义的别名，改用HAVING可以直接用别名筛选（适用于MySQL 5.7+，或关闭ONLY_FULL_GROUP_BY模式）：

SELECT name, TIMESTAMPDIFF(YEAR, birthday, CURDATE()) AS age
FROM personnel
HAVING age BETWEEN 18 AND 25;

写法三：子查询包装 #

通过子查询先算出年龄，再在外层筛选：

SELECT name, age
FROM (
    SELECT name, TIMESTAMPDIFF(YEAR, birthday, CURDATE()) AS age
    FROM personnel
) AS temp_table
WHERE age BETWEEN 18 AND 25;

内容的提问来源于stack exchange，提问作者Alex