如果相關表上存在id，如何查詢不包含數據的表？

Question

這是我的桌子。

通知表

+----+--------------+
| Id | Subject      |
+----+--------------+
| 1  | Loreum Ipsum |
| 2  | Hello World  |
| 3  | Pls Help     |
+----+--------------+

用戶通知表

+----+----------------+--------+
| Id | NotificationId | Status |
+----+----------------+--------+
| 1  | 1              | Read   |
+----+----------------+--------+

如果UserNotification表上存在NotificationId我想查詢通知表而不包含數據

我想要結果：

通知表

+----+-------------+
| Id | Subject     |
+----+-------------+
| 2  | Hello World |
| 3  | Pls Help    |
+----+-------------+

Answer 1

使用NOT EXISTS

詢問

SELECT * FROM Notification n
WHERE NOT EXISTS(
    SELECT 1 FROM UserNotification u
    WHERE n.Id = u.NotificationId
);

sql fiddle demo

Answer 2

你可以不用

select Id,Subject from notificationTable
where Id not in (select Id from userNotificationTable) ;

Answer 3

您還可以使用JOIN ：

SELECT n.*
FROM Notification n
JOIN UserNotification un
ON n.Id <> un.NotificationId

SQLFiddle演示

Answer 4

你可以做..

Select * from Notification
left join UserNotification on Notification.id = UserNotification.NotificationId
where UserNotification.id is null

SQLFiddle

Answer 5

您可以使用NULL檢查通過LEFT JOIN實現：

SELECT N.Id, N.Subject
FROM `Notification` N
LEFT JOIN `UserNotification` U ON U.NotificationId = N.Id
WHERE U.NotificationId IS NULL

Answer 6

使用NOT IN

Select * from Notification where id NOT IN (SELECT id FROM UserNotification)

這個SQL將有助於獲取數據

Answer 7

SELECT n.Id, n.Subject FROM Notification n
LEFT JOIN UserNotification nu on nu.NotificationId = n.id
WHERE nu.id IS NULL

Answer 8

您想要返回用戶通知中沒有的通知

嘗試這個 ：

select Id,Subject
from Notification  
where 
id not in (
select distinct NotificationId  from UserNotification
)