php - 如果相关表上存在id，如何查询表不包含数据？

Question

这是我的表格。

通知表

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

用户通知表

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

如果 UserNotification 表上存在 NotificationId，我想查询不包括数据的通知表

我要结果:

通知表

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

Answer 1

使用NOT EXISTS

查询

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

sql fiddle demo