为什么不允许MERGE语句的目标表启用规则？

Question

我们有一个更新数据库的进程,它使用以下SQL

IF NOT EXISTS (SELECT * FROM Target_Table WHERE Target_Table_ID = ...)
BEGIN
    INSERT ...
END
ELSE
BEGIN
    UPDATE ...
END

我想改变它以使用一个MERGE语句,以避免可能的竞争条件,其中单独评估IF和然后INSERT或UPDATE语句.

但是,只要我执行查询,我就会收到错误:

MERGE语句的目标表'Target_Table'不能具有任何已启用的规则.找到规则'TargetTable_RULE'

我理解文档声明该表不能启用规则,虽然我在第一次阅读时错过了它,除了在执行之前禁用规则MERGE(我不认为这是一个可行的解决方案),似乎我坚持该IF NOT EXISTS解决方案.

该文件没有解释的是为什么目标表不允许有规则.在我的情况下,规则是> 0对值的简单检查.

有谁知道为什么在这种情况下不允许规则,是否有另一种方式以原子方式执行upsert？

编辑:正如Andriy M评论的问题SQL Server 2005中的Atomic UPSERT已经有大量关于原子upserts的信息,所以我不会在这里重复讨论.相反,我只想知道为什么MERGE语句无法在已定义规则的表上执行,是否有解决方法？

Answer 1

• 规则是SQL Server的旧功能.
• 将在Microsoft SQL Server的未来版本中删除此功能..我认为,这就是为什么MERGE语句不支持带规则的表的原因.
• 您可以使用检查约束替换规则.

MERGE示例(带有规则和CHECK约束):

CREATE RULE MyRule
AS 
@Status IN ('Y', 'N');
GO

CREATE TABLE dbo.SalesOrder
(
    SalesOrderID INT PRIMARY KEY
    ,OrderDate DATETIME NOT NULL
    ,IsDeleted CHAR(1) NOT NULL DEFAULT 'N'
);
GO

EXEC sp_bindrule @rulename='MyRule', @objname='dbo.SalesOrder.IsDeleted';
GO

INSERT  dbo.SalesOrder (SalesOrderID, OrderDate)
SELECT  1, '20110101'
UNION ALL
SELECT  2, '20110202'
UNION ALL
SELECT  3, '20110303';
GO

SELECT  *
FROM    dbo.SalesOrder;

PRINT '*****First test*****';
GO

MERGE   dbo.SalesOrder Dst
USING   (VALUES (1,'Y'), (4,'Y')) AS Src(SalesOrderID, IsDeleted) 
ON      Dst.SalesOrderID = Src.SalesOrderID
WHEN    MATCHED THEN UPDATE SET IsDeleted = Src.IsDeleted
WHEN    NOT MATCHED BY TARGET THEN INSERT (SalesOrderID, OrderDate, IsDeleted) VALUES (Src.SalesOrderID, GETDATE(), Src.IsDeleted);
GO

EXEC sp_unbindrule 'dbo.SalesOrder.IsDeleted'; --Disabling `MyRule` for IsDeleted column
ALTER TABLE dbo.SalesOrder --We "replace" the old rule with a new `CHECK` constraint
ADD CONSTRAINT CK_SalesOrder_IsDeleted CHECK( IsDeleted IN ('Y', 'N') );
GO

PRINT '*****Second test*****';
MERGE   dbo.SalesOrder Dst
USING   (VALUES (1,'Y'), (4,'Y')) AS Src(SalesOrderID, IsDeleted) 
ON      Dst.SalesOrderID = Src.SalesOrderID
WHEN    MATCHED THEN UPDATE SET IsDeleted = Src.IsDeleted
WHEN    NOT MATCHED BY TARGET THEN INSERT (SalesOrderID, OrderDate, IsDeleted) VALUES (Src.SalesOrderID, GETDATE(), Src.IsDeleted);
GO

SELECT  *
FROM    dbo.SalesOrder;

DROP TABLE dbo.SalesOrder;
DROP RULE MyRule;

结果:

Rule bound to table column.

(3 row(s) affected)
SalesOrderID OrderDate               IsDeleted
------------ ----------------------- ---------
1            2011-01-01 00:00:00.000 N
2            2011-02-02 00:00:00.000 N
3            2011-03-03 00:00:00.000 N

(3 row(s) affected)

*****First test*****
Msg 358, Level 16, State 1, Line 2
The target table 'Dst' of the MERGE statement cannot have any enabled rules.  Found rule 'MyRule'.
Rule unbound from table column.
*****Second test*****

(2 row(s) affected)
SalesOrderID OrderDate               IsDeleted
------------ ----------------------- ---------
1            2011-01-01 00:00:00.000 Y
2            2011-02-02 00:00:00.000 N
3            2011-03-03 00:00:00.000 N
4            2011-09-20 16:03:56.030 Y

(4 row(s) affected)