检测SQL中的循环引用

我有下表：

CREATE TABLE X (
    A SOMETYPE NOT NULL,
    B SOMETYPE NOT NULL,
    C SOMETYPE NULL,
    PRIMARY KEY (A,B),
    FOREIGN KEY (A,C) REFERENCES X (A,B)
);

存储在

X

中的实体是分层组织的：如果行

（A1，B1，C1）

存在并且

C1不为空

，则它被视为

（A1，C1，C2）

的“子级”。由于项目不能从自身下降，我想将循环层次序列的存在定为非法：

-- legal
INSERT INTO X (A1,B1,NULL);
INSERT INTO X (A1,B2,B1);
INSERT INTO X (A1,B3,B2);
INSERT INTO X (A1,B4,B2);

-- currently legal, but I want to make it illegal
UPDATE X SET C = B1 WHERE B = B1;  /* B1-B1 */
UPDATE X SET C = B2 WHERE B = B1;  /* B1-B2-B1 */
UPDATE X SET C = B3 WHERE B = B1;  /* B1-B2-B3-B1 */
UPDATE X SET C = B4 WHERE B = B1;  /* B1-B2-B4-B1 */
UPDATE X SET C = B2 WHERE B = B2;  /* B2-B2 */
UPDATE X SET C = B3 WHERE B = B2;  /* B2-B3-B2 */
UPDATE X SET C = B4 WHERE B = B2;  /* B2-B4-B2 */
UPDATE X SET C = B3 WHERE B = B3;  /* B3-B3 */
UPDATE X SET C = B4 WHERE B = B4;  /* B4-B4 */

我该怎么做

---

或者，我可以将表示层次结构中“级别”的字段添加到表中：

CREATE TABLE X (
    A SOMETYPE NOT NULL,
    B SOMETYPE NOT NULL,
    C SOMETYPE NULL,
    LEVEL INT NOT NULL,
    PRIMARY KEY (A,B),
    FOREIGN KEY (A,C) REFERENCES X (A,B)
);

然后，我想要求

LEVEL

在

C为NULL

时为

0

，否则为

parent的LEVEL+1

---

---

我正在使用SQL Server 2008 R2。

为了检查循环引用，我使用了触发器和递归CTE：

CREATE TRIGGER trgIU_X_CheckCircularReferences
ON dbo.X
AFTER INSERT, UPDATE 
AS
BEGIN   
    SET NOCOUNT ON;
    DECLARE @Results TABLE ([Exists] BIT);

    WITH CteHierarchy
    AS
    (
        SELECT  x.A, x.B, X.C, 1 AS [Type]
        FROM    inserted i
        JOIN    X x ON i.A = x.A AND i.C = x.B
        UNION ALL
        SELECT  x.A, x.B, X.C, 2 AS [Type]
        FROM    CteHierarchy i
        JOIN    X x ON i.A = x.A AND i.C = x.B
        WHERE   NOT EXISTS 
        (
                SELECT  *
                FROM    inserted a
                WHERE   a.A = x.A AND a.B = x.B
        )   
    )
    INSERT  @Results ([Exists])
    SELECT  TOP(1) 1
    FROM    CteHierarchy h
    JOIN    X x ON h.A = x.A AND h.C = x.B
    OPTION(MAXRECURSION 1000);

    IF EXISTS(SELECT * FROM @Results)
    BEGIN
        ROLLBACK;
        RAISERROR('Circular references detected', 16, 1);
    END
END
GO

现在，我们可以运行一些测试：

--Test 1 - OK
PRINT '*****Test 1 - OK*****';
SELECT * FROM X;

BEGIN TRANSACTION;

UPDATE  X 
SET     C = 'B1'
WHERE   B = 'B4';

SELECT * FROM X;

--This transaction can be commited without problems
--but I will cancel all modification so we can run the second test
ROLLBACK TRANSACTION;
PRINT '*****End of test 1*****';    
GO

--Test 2 - NOT OK
PRINT '*****Test 2 - NOT OK*****';
SELECT * FROM X;

BEGIN TRANSACTION;

UPDATE  X 
SET     C = 'B1'
WHERE   B = 'B1';

--Useless in this case (test 2 & test 3)
--Read section [If a ROLLBACK TRANSACTION is issued in a trigger] from http://msdn.microsoft.com/en-us/library/ms181299.aspx
SELECT * FROM X;
--Useless
ROLLBACK TRANSACTION;
--Useless
PRINT '*****End of test 2*****';        
GO

PRINT '*****Test 3 - NOT OK*****';
SELECT * FROM X;

BEGIN TRANSACTION;

UPDATE  X 
SET     C = 'B4'
WHERE   B = 'B1';
GO

结果:

*****Test 1 - OK*****

(4 row(s) affected)

(0 row(s) affected)

(1 row(s) affected)

(4 row(s) affected)
*****End of test 1*****
*****Test 2 - NOT OK*****

(4 row(s) affected)

(1 row(s) affected)
Msg 50000, Level 16, State 1, Procedure trgIU_X_CheckCircularReferences, Line 34
Circular references detected
Msg 3609, Level 16, State 1, Line 8
The transaction ended in the trigger. The batch has been aborted.
*****Test 3 - NOT OK*****

(4 row(s) affected)

(1 row(s) affected)
Msg 50000, Level 16, State 1, Procedure trgIU_X_CheckCircularReferences, Line 34
Circular references detected
Msg 3609, Level 16, State 1, Line 7
The transaction ended in the trigger. The batch has been aborted.

---

对于第二个测试，您可以看到此触发器如何取消（

回滚事务

）事务，并且在更新后，没有执行任何操作（在当前批处理中）。

哪个DBMS？SQL Server 2000/2005/2008、Oracle、MySQL等？SQL Server 2008。。。我不认为这有什么关系，当然有关系。如果一个新功能可以解决这个问题呢？你能提供下表中的实际数据示例吗？我很难想象这样的业务场景。@foampile：我正在制作一个工具，用于将任意业务流程表示为一系列事务，这些事务以预先指定的格式操作文档。基本上，一个元数据数据库，其内容从事务的角度完全指定了ERP。现在，我不再使用SQL Server（或任何SQL DBMS）。我正在制作自己的数据库管理系统。