本文介绍了联接中的负条件的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
是否有更好的方法(性能或语法)编写以下mysql查询:
Is there a better way (performance or syntax) to write the following mysql query:
Select un.user_id
from user_notifications un
where un.notification_id = 'xxxxyyyyyzzzz'
and un.user_id not in (Select user_id from user_push_notifications upn
where upn.notification_id = 'xxxxyyyyyzzzz') ;
目的是查找尚未被推送通知的那些user_id特定的notification_id
The purpose is to find those user_id which have not been pushed a notification for a certain notification_id
推荐答案
您可以尝试以下方法，它与@Abhik的第一个答案相同，但有更多条件.
You can try the following, it is same as @Abhik's first answer but with one more condition.
SELECT DISTINCT un.user_id -- This will give you unique users
FROM user_notifications un
LEFT JOIN
user_push_notifications upn
ON
upn.user_id = un.user_id
AND upn.notification_id = "xyz" -- This will match with un by user_id for a specific notifioncation id.
WHERE un.notification_id = "xyz" -- This will get only the specific notifications.
AND upn.notification_id IS null; -- This will make sure that all the user_ids are filtered which exist in upn with specific notification id.
这篇关于联接中的负条件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！