Question

我在这里有这么大的查询：

select
 user_contact_id as userContactId,
 max(attempt_number) as attemptNumber,
 max(sent_timestamp) as sentTimestamp,
 source as source,
 from
    share_email_tracking `set`
 group by
    user_contact_id
 having
     (attemptNumber = 1 and date_sub(CURDATE(), interval 4 day) >= date(sentTimestamp))

问题是，我实际上对attemptNumber或sentTimestamp不感兴趣。我只需要那些来计算“having”子句。我不知道有任何语法可以做到这一点，我认为这是一个比“拥有”更普遍的问题所以我无法在文档中找到它。我相信临时变量是可能的，但据我所知，这些是特定于会话的，而不是特定于查询的，我不希望它们污染状态。这可能吗？

在现实生活中，我多次复制sentTimestamp所以我应该避免将其替换为原始版本。

Answer 1

您可以将它们放在Having中。只需使用实际表达式而不是别名。

select  user_contact_id as userContactId,
        source as source

from    share_email_tracking `set`

group by user_contact_id

having (max(attempt_number) = 1 and date_sub(CURDATE(), interval 4 day) >= max(sent_timestamp))

如果您想要别名表达式，则可以执行此操作，这样您就不必在having子句中多次写入它们。创建一个子选择，然后使用主查询的WHERE子句中的别名。

select  userContactId, source

FROM

(

 select  user_contact_id as userContactId,
         max(attempt_number) as attemptNumber,
         max(sent_timestamp) as sentTimestamp,
         source as source

 from    share_email_tracking `set`

 group by user_contact_id

) as x

WHERE    (attemptNumber = 1 and date_sub(CURDATE(), interval 4 day) >= date(sentTimestamp))

Answer 2

你可以在where子句

中完成它们

   select
 user_contact_id as userContactId,
 max(attempt_number) as attemptNumber,
 max(sent_timestamp) as sentTimestamp,
 source as source,
from
   share_email_tracking `set`

group by
user_contact_id
HAVING  max(attempt_number) = 1  AND date(sentTimestamp) <= date_sub(CURDATE(), interval 4 day)

如何在没有选择的情况下在“having”子句中使用变量？

2 个答案: