ON DELETE CASCADE 删除额外的行

Question

我有以下表格：

CREATE TABLE workspace (
    id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    uid VARCHAR(255),
    name NVARCHAR(255)
);

CREATE TABLE userGroup (
    id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    workspaceId INT,
    FOREIGN KEY (workspaceId) REFERENCES workspace(id) ON DELETE CASCADE,
    name NVARCHAR(255)
);

CREATE TABLE userWorkspaceMapping (
    id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    workspaceId INT,
    FOREIGN KEY (workspaceId) REFERENCES workspace(id) ON DELETE CASCADE,
    userId INT,
    FOREIGN KEY (userId) REFERENCES user(id),
    userGroupId INT,
    FOREIGN KEY (userGroupId) REFERENCES userGroup(id) ON DELETE CASCADE
);

userWorkspaceMapping 的数据：

+----+-------------+--------+-------------+
| id | workspaceId | userId | userGroupId |
+----+-------------+--------+-------------+
| 1  |      1      |    1   |      1      |    <------- I want to delete only this row
| 2  |      2      |    1   |      3      |
| 3  |      3      |    1   |      5      |
+-----------------------------------------+

当我删除 workspace 时，userWorkspaceMapping 中的所有三行都被删除，而不仅仅是第一行。

delete from workspace
where id = 1;

为什么 userWorkspaceMapping 中的所有内容都被删除了？

这是 fiddle：https://www.db-fiddle.com/f/tHMZy2rnyvoHH13E7dS99A/1

Answer 1

您的 userGroup table 还引用了带有 ON DELETE CASCADE 约束的 workspace。因此，当您在工作区中删除一行时，userGroup 中引用它的所有行都将被删除。

这意味着第 1 组到第 5 组已删除。

mysql> delete from workspace where id = 1;
Query OK, 1 row affected (0.03 sec)

mysql> 
mysql> select * from userGroup;
+----+-------------+------+
| id | workspaceId | name |
+----+-------------+------+
|  6 |           2 | b1   |
|  7 |           2 | b2   |
|  8 |           2 | b3   |
|  9 |           2 | b4   |
| 10 |           2 | b5   |
| 11 |           3 | c1   |
| 12 |           3 | c2   |
| 13 |           3 | c3   |
| 14 |           3 | c4   |
| 15 |           3 | c5   |
+----+-------------+------+

因此，userWorkspaceMapping 中引用组 1 到 5 的所有行都将被删除。这占所有行。

级联可以并且确实在外键引用中级联了不止一个“步骤”。

Answer 2

CASCADE实际上没有问题...我在这里插入了错误的测试 ID:

INSERT INTO userWorkspaceMapping (
  userId,
  workspaceId,
  userGroupId
)
VALUES 
  (1, 1, 1),
  (1, 2, 3),  -- <---- should be between 6 and 9
  (1, 3, 5)   -- <---- should be between 10 and 15
 ;

它们都属于已删除的工作区...ID 应该是正确的。

ON DELETE CASCADE 删除额外的行

ON DELETE CASCADE deletes extra rows

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foreign-keys

cascade