同一个 table 上的两个外键：删除级联如何实现？

Question

我有一个包含两列的 table。他们每个人都是同一秒的外键 table:

CREATE TABLE [dbo].[TBL_TOGETHER]
(
    [ID1] [int] NULL FOREIGN KEY REFERENCES [TBL_ANOTHER_TABLE](ID),
    [ID2] [int] NULL FOREIGN KEY REFERENCES [TBL_ANOTHER_TABLE](ID)
)

但现在我不能再从 TBL_ANOTHER_TABLE 中删除实体了：

The DELETE statement conflicted with the REFERENCE constraint "FK__TBL_ASD__4DE98D56".

我的问题是：在 TBL_TOGETHER 实施 ON DELETE CASCADE 的最佳解决方案是什么？

我尝试在外键上添加ON DELETE SET NULL或ON DELETE CASCADE，但由于循环或多个级联路径，它不起作用。

我尝试在TBL_ANOTEHR_TABLE上添加删除触发器，但它仍然与外键冲突：

ALTER TRIGGER REMOVE_FORENGKEY
ON TBL_ANOTHER_TABLE 
FOR DELETE
AS
BEGIN
    UPDATE TBL_TOGETHER
    SET TBL_TOGETHER.ID1 = NULL
    FROM TBL_TOGETHER
    JOIN deleted ON TBL_TOGETHER.ID1 = deleted.ID;

    UPDATE TBL_TOGETHER
    SET TBL_TOGETHER.ID2 = NULL
    FROM TBL_TOGETHER
    JOIN deleted ON TBL_TOGETHER.ID2 = deleted.ID;
END

我试过 INSTEAD OF DELETE 触发器，但这种方法也不起作用，因为引用的 table 还包含一个具有级联约束的外键。

ALTER TRIGGER REMOVE_FORENGKEY
ON TBL_ANOTHER_TABLE 
INSTEAD OF DELETE
AS
BEGIN
    UPDATE TBL_TOGETHER
    SET TBL_TOGETHER.ID1 = NULL
    FROM TBL_TOGETHER
    JOIN deleted ON TBL_TOGETHER.ID1 = deleted.ID;

    UPDATE TBL_TOGETHER
    SET TBL_TOGETHER.ID2 = NULL
    FROM TBL_TOGETHER
    JOIN deleted ON TBL_TOGETHER.ID2 = deleted.ID;

    DELETE TBL_ANOTHER_TABLE 
    FROM TBL_ANOTHER_TABLE 
    JOIN deleted ON TBL_ANOTHER_TABLE.ID = deleted.ID 
    WHERE TBL_ANOTHER_TABLE.ID = deleted.ID;
END

错误：

Cannot alter INSTEAD OF DELETE or INSTEAD OF UPDATE TRIGGER 'REMOVE_FORENGKEY' on table 'TBL_ANOTHER_TABLE '. This is because the table has a FOREIGN KEY with cascading DELETE or UPDATE.

Answer 1

使用这个触发器：此触发器起作用而不是删除。因此您必须在将引用设置为空后删除记录。

 CREATE TRIGGER Trigger_TBL_ANOTHER_TABLE
    ON [dbo].[TBL_ANOTHER_TABLE]
    INSTEAD OF DELETE
    AS 
    BEGIN

        SET NOCOUNT ON;

        UPDATE  t
        SET     t.ID1 = NULL
        from [dbo].[TBL_TOGETHER] t inner join
        deleted d on d.ID = t.ID1

        UPDATE  t
        SET     t.ID2 = NULL
        from [dbo].[TBL_TOGETHER] t inner join
        deleted d on d.ID = t.ID2

        DELETE  t
        from [dbo].[TBL_ANOTHER_TABLE] t inner join
        deleted d on d.ID = t.ID

    END
    GO

同一个 table 上的两个外键：删除级联如何实现？

Two foreign keys on same table: how to implement on delete cascade?

sql-server

ddl

foreign-keys