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

我想将此更改为使用MERGE语句，以避免可能的竞争条件，其中IF然后INSERT或UPDATE语句将单独计算。

但是，只要我执行了查询，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'

我理解文档说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MERGE之前禁用规则（我认为这不是一个可行的解决方案））似乎我坚持使用IF NOT EXISTS解决方案。

该文档未解释的是为什么目标表不允许有规则。在我的情况下，规则是对值的简单> 0检查。

有没有人知道为什么在这种情况下不允许使用规则，以及是否有其他方式以原子方式执行upsert？

编辑：正如Andriy M评论的问题Atomic UPSERT in SQL Server 2005已经有关于原子upsert的大量信息所以我不会在这里重复讨论。相反，我想知道为什么MERGE语句无法在已定义规则的表上执行，是否有解决办法？

Answer 1

规则是SQL Server的旧功能。
This feature will be removed in a future version of Microsoft SQL Server.。我认为，这就是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CHECK约束的规则＆amp;）：

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)

为什么不允许MERGE语句的目标表启用规则？

1 个答案: