MySQL别名子查询不能用在where子句中

Question

我有一个查询如下，返回所有要求的数据。然后在我需要写的下一个查询中，我需要限制输出到子查询大于5的位置。

我将显示示例，但我无法理解为什么我无法执行所尝试的操作。

查询不受限制

select t1.BOOK_NUM, t1.BOOK_TITLE, 
(select count(t2.CHECK_OUT_DATE) 
from checkout t2 
where t2.BOOK_NUM = t1.BOOK_NUM) as Times_Checked_Out 
from book t1 
order by Times_Checked_Out desc, t1.BOOK_TITLE; 

输出的屏幕截图

尝试在与限制查询

select t1.BOOK_NUM, t1.BOOK_TITLE, 
(select count(t2.CHECK_OUT_DATE) 
from checkout t2 
where t2.BOOK_NUM = t1.BOOK_NUM) as Times_Checked_Out 
from book t1 
where Times_Checked_Out > 5 
order by Times_Checked_Out desc, t1.BOOK_TITLE; 

错误

Answer 1

你不能在where子句中使用派生列，需要使用HAVING：

select t1.BOOK_NUM, t1.BOOK_TITLE, 
(select count(t2.CHECK_OUT_DATE) 
from checkout t2 
where t2.BOOK_NUM = t1.BOOK_NUM) as Times_Checked_Out 
from book t1 
HAVING Times_Checked_Out > 5 
order by Times_Checked_Out desc, t1.BOOK_TITLE;