Question

MS SQL是否使用ON DELETE CASCADE选项限制自引用约束？我有一个父子关系表，PARENT_ID列是ID的外键。使用ON DELETE CASCADE选项创建它会导致错误

“引入FOREIGN KEY约束可能导致循环或多个级联路径。指定ON DELETE NO ACTION或 ON UPDATE NO ACTION，或修改其他 FOREIGN KEY约束。“

我无法相信我必须在递归模式下删除此层次结构。除了触发器有什么问题吗？

Answer 1

无法在具有自引用约束的表上设置ON DELETE CASCADE。存在潜在的周期性逻辑问题，因此它不会允许它。

有一篇好文章here - 虽然它适用于版本8而不是9版SQL - 尽管适用相同的规则。

Answer 2

我刚回答another question 这个问题被绑定为重复。我认为值得在这里提出我的答案：

这是不可能的。您可以使用INSTEAD OF TRIGGER

解决此问题

create table locations 
(
    id int identity(1, 1),
    name varchar(255) not null,
    parent_id int,

    constraint pk__locations
        primary key clustered (id)

)
GO

INSERT INTO locations(name,parent_id)  VALUES
 ('world',null)
,('Europe',1)
,('Asia',1)
,('France',2)
,('Paris',4)
,('Lyon',4);
GO

- 此触发器将使用递归CTE获取您要删除的所有ID之后的所有ID。这些ID将被删除。

CREATE TRIGGER dbo.DeleteCascadeLocations ON locations
INSTEAD OF DELETE 
AS
BEGIN
    WITH recCTE AS
    (
        SELECT id,parent_id
        FROM deleted

        UNION ALL

        SELECT nxt.id,nxt.parent_id
        FROM recCTE AS prv
        INNER JOIN locations AS nxt ON nxt.parent_id=prv.id
    )
    DELETE FROM locations WHERE id IN(SELECT id FROM recCTE);
END
GO

- 在此测试，尝试使用不同的ID。您也可以尝试WHERE id IN(4,3) ...

SELECT * FROM locations;

DELETE FROM locations WHERE id=4;

SELECT * FROM locations
GO

- 清理（仔细查看真实数据！）

if exists(select 1 from INFORMATION_SCHEMA.TABLES where TABLE_NAME='locations')
---DROP TABLE locations;

Answer 3

CREATE TRIGGER MyTable_OnDelete ON MyTable
INSTEAD OF DELETE
AS 
BEGIN

  SET NOCOUNT ON;

  DELETE FROM mt
  FROM   deleted AS D
  JOIN   MyTable AS mt
  ON     d.Id = mt.ParentId

  DELETE FROM mt
  FROM   deleted AS D
  JOIN   MyTable AS mt
  ON     d.Id = mt.Id

END

MS SQL中的自引用约束

3 个答案: