MySQL别名子查询不能在where子句

Question

我在下面给出了一个查询，它返回所有要求的数据。然后在我需要编写的下一个查询中，我需要将输出限制为子查询大于5的位置。

我会展示一些例子，但我无法理解为什么我不能做我正在尝试的事情。

无限制查询

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
order by Times_Checked_Out desc, t1.BOOK_TITLE;

输出截图

尝试使用限制查询

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

您不能在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;