复合主键和外键约束错误

Question

我有一个SQL表定义如下:

CREATE TABLE [TestComposite] (  
    ID int,  
    SiteUrl nvarchar(255),  
    Name nvarchar(max) NOT NULL,  
    ParentID int NULL,  
    PRIMARY KEY (ID, SiteUrl)  
);

项目和文件夹存储在同一个表中,如果项目位于文件夹内,则ParentID列是文件夹的ID.我希望能够在删除文件夹时删除CASCADE项目/文件夹.

一个例子可能更明确:

INSERT INTO [TestComposite] VALUES (1, 'site1', 'Item1', NULL)
INSERT INTO [TestComposite] VALUES (2, 'site1', 'Item2', NULL)
INSERT INTO [TestComposite] VALUES (3, 'site1', 'Folder1', NULL)
INSERT INTO [TestComposite] VALUES (4, 'site1', 'Folder1.Item1', 3)
INSERT INTO [TestComposite] VALUES (5, 'site1', 'Folder1.Item2', 3)
INSERT INTO [TestComposite] VALUES (6, 'site1', 'Folder1.Folder1', 3)
INSERT INTO [TestComposite] VALUES (7, 'site1', 'Folder1.Folder1.Item1', 6)
etc...

因此,如果我删除项目3(文件夹),我也希望删除项目/文件夹4,5,6和7.

我试图添加一个类似于的约束:

ALTER TABLE [TestComposite] 
ADD CONSTRAINT fk_parentid 
FOREIGN KEY (ParentID, SiteUrl) 
REFERENCES [TestComposite] (ID, SiteUrl) ON DELETE CASCADE;

但它给了我这个错误:
在表'TestComposite'上引入FOREIGN KEY约束'fk_parentid'可能会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.

我还尝试添加名为ParentSiteUrl的第二个SiteUrl列,以防问题是列不属于同一个FK/PK,但我有相同的错误消息.

难道我做错了什么？

谢谢,

Answer 1

创建一个ON DELETE NO ACTION约束并使用它来删除所有记录及其子项:

WITH    q AS
        (
        SELECT  id, SiteURL
        FROM    TestComposite
        WHERE   id = 3
                AND SiteURL = 'site1'
        UNION ALL
        SELECT  tc.id, tc.SiteURL
        FROM    q
        JOIN    TestComposite tc
        ON      tc.ParentID = q.Id
                AND tc.SiteURL = q.SiteURL
        )
DELETE
FROM    TestComposite
WHERE   EXISTS
        (
        SELECT  id, SiteURL
        INTERSECT
        SELECT  *
        FROM    q
        )