sql-server-2008 - 为什么 MERGE 语句的目标表不允许有启用的规则？

Question

我们有一个使用以下 SQL 更新数据库的进程

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

我想将其更改为使用 MERGE 语句以避免可能的竞争条件，其中 IF 然后是 INSERT 或 UPDATE 语句单独计算。

但是，当我执行查询时，我得到了错误:

The target table 'Target_Table' of the MERGE statement cannot have any enabled rules. Found rule 'TargetTable_RULE'

我理解文档指出该表不能启用规则，虽然我在第一次阅读它时错过了它，除了在执行 MERGE 之前禁用规则(我不认为一个可行的解决方案)似乎我坚持使用 IF NOT EXISTS 解决方案。

文档没有解释的是为什么目标表不允许有规则。在我的例子中，规则是一个简单的 > 0 检查值。

有谁知道为什么在这种情况下不允许使用规则，以及是否有其他方法以原子方式执行更新插入？

编辑: 正如 Andriy M 评论的问题 Atomic UPSERT in SQL Server 2005已经有大量关于原子更新插入的信息，所以我不会在这里重复讨论。相反，我只想知道为什么 MERGE 语句无法在定义了规则的表上执行，是否有解决方法？

Answer 1

• 规则是 SQL Server 的旧功能。
• This feature will be removed in a future version of Microsoft SQL Server. .我想，这就是为什么 MERGE 语句不支持带规则的表的原因。
• 您可以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)