如何在「having」子句中使用變量而不選擇它？

Question

我在這裏有這樣大的查詢：

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)) 

問題是，我沒有真正感興趣attemptNumber或sentTimestamp。我只需要那些來計算「有」條款。我不知道這樣做的任何語法，我認爲這是一個比「擁有」更普遍的問題，所以我一直無法在它的文檔中找到它。我相信臨時變量是可能的，但據我所知，這些是會話特定的，而不是特定於查詢的，我不希望它們污染狀態。這可能嗎？

在現實生活中，我複製了sentTimestamp幾次，所以我應該避免僅僅用它來代替它。

Answer 1

你可以做他們在where子句

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) 

Answer 2

你可以只把它們放在你的Having。只需使用實際的表達式而不是別名。

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)) 

，如果你想表達的別名，這樣你就不必他們多次寫having子句您在你能做到這一點。創建一個子選擇，然後使用主查詢的WHERE子句中的別名。

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))