我正在运行的查询如下，但是我收到了这个错误：

1054 - ‘IN/ALL/ANY 子查询’中的未知列 ‘guaranteed_postcode’

SELECT `users`.`first_name`, `users`.`last_name`, `users`.`email`,
SUBSTRING(`locations`.`raw`,-6,4) AS `guaranteed_postcode`
FROM `users` LEFT OUTER JOIN `locations`
ON `users`.`id` = `locations`.`user_id`
WHERE `guaranteed_postcode` NOT IN #this is where the fake col is being used
(
 SELECT `postcode` FROM `postcodes` WHERE `region` IN
 (
  'australia'
 )
)

我的问题是：为什么我不能在同一个数据库查询的 where 子句中使用假列？