Question

我有以下查询。逻辑上，过程usp_mytran应该将表dbo.Sales的标识重置为1。但是最后一个查询为 Max_ID_Value 和 Current_Seed_Value 返回了不同的值。任何人都可以解释为什么DBCC命令在程序内部无效？

USE tempdb

--  Create table 
CREATE  TABLE dbo.Sales
(ID INT IDENTITY(1,1), Address VARCHAR(200))
GO

--  Procedure to Populate data into dbo.Sales
CREATE PROCEDURE usp_mytran 
AS
BEGIN
BEGIN TRANSACTION
    INSERT dbo.Sales
            ( Address )
    VALUES  ( 'Dwarka, Delhi' );

    --  Delete it for some reason
    DELETE FROM dbo.Sales;

    --  Code to check max ID value, and verify it again IDENTITY SEED
    DECLARE @MaxValue INT = (SELECT ISNULL(MAX(ID),1) FROM dbo.Sales)
    IF @MaxValue IS NOT NULL AND @MaxValue <> IDENT_CURRENT('dbo.Sales')
        DBCC CHECKIDENT ( 'tempdb.dbo.Sales', RESEED, @MaxValue );
ROLLBACK TRANSACTION
END

--  Ideally, this should RESEED the Identity of dbo.Sales table.
EXEC usp_mytran

--  Max_ID_Value & Current_Seed_Value should be same
SELECT ISNULL(MAX(ID),1) AS Max_ID_Value, IDENT_CURRENT('dbo.Sales') AS Current_Seed_Value FROM dbo.Sales

Answer 1

很抱歉回答我自己的问题。正如@Kannan Kandasamy指出的那样，ROLLBACK TRANSACTION代码正在恢复DBCC CHECKIDENT所完成的工作。因此，为了使其工作，我创建了一个名为Reseed_Sales的作业，其中包含表dbo.Sales的RESEED Identity的代码。以下是程序usp_mytran的最终查询。

--  Procedure to Populate data into dbo.Sales
ALTER PROCEDURE usp_mytran 
AS
BEGIN
BEGIN TRANSACTION
    INSERT dbo.Sales
            ( Address )
    VALUES  ( 'Dwarka, Delhi' );

    --  Delete it for some reason
    DELETE FROM dbo.Sales;

    --  Code to check max ID value, and verify it again IDENTITY SEED
    DECLARE @MaxValue INT = (SELECT ISNULL(MAX(ID),1) FROM dbo.Sales)
    IF @MaxValue IS NOT NULL AND @MaxValue <> IDENT_CURRENT('dbo.Sales')
        EXEC msdb..sp_start_job @job_name = 'Reseed_Sales'
ROLLBACK TRANSACTION
END

Answer 2

实际上它在存储过程中按预期工作：Rollback tran将回滚checkident值 - 这就是代码中发生的事情

--  Procedure to Populate data into dbo.Sales
alter PROCEDURE usp_mytran 
AS
BEGIN
    BEGIN TRANSACTION
    INSERT dbo.Sales
            ( Address )
    VALUES  ( 'Dwarka, Delhi' );

    --  Delete it for some reason
    DELETE FROM dbo.Sales;

    --  Code to check max ID value, and verify it again IDENTITY SEED
    DECLARE @MaxValue INT = (SELECT ISNULL(MAX(ID),1) FROM dbo.Sales)
    IF @MaxValue IS NOT NULL AND @MaxValue <> IDENT_CURRENT('test.dbo.Sales')
        DBCC CHECKIDENT ( 'test.dbo.Sales', RESEED, @MaxValue );
    ROLLBACK TRANSACTION
END

如果你现在检查ident_current它显示2并且在下一次运行时它显示4等因为 ROLLBACK TRANSACTION

现在在多次执行后检查＆＃34; EXEC usp_mytran＆＃34;

select IDENT_CURRENT('test.dbo.Sales')

您将看到checkident不会重置。

如果我们删除该事务，则CHECKIDENT将重新设置为1。

以下评论的交易

--  Procedure to Populate data into dbo.Sales
alter PROCEDURE usp_mytran 
AS
BEGIN
    --BEGIN TRANSACTION
    INSERT dbo.Sales
            ( Address )
    VALUES  ( 'Dwarka, Delhi' );

    --  Delete it for some reason
    DELETE FROM dbo.Sales;

    --  Code to check max ID value, and verify it again IDENTITY SEED
    DECLARE @MaxValue INT = (SELECT ISNULL(MAX(ID),1) FROM dbo.Sales)
    IF @MaxValue IS NOT NULL AND @MaxValue <> IDENT_CURRENT('test.dbo.Sales')
        DBCC CHECKIDENT ( 'test.dbo.Sales', RESEED, @MaxValue );
    --ROLLBACK TRANSACTION
END

现在在多次执行后检查＆＃34; EXEC usp_mytran＆＃34;

select IDENT_CURRENT('test.dbo.Sales')

您会看到重新设定的值为＆＃39; 1＆＃39;

检查以下示例......

Can we rollback to original state after we have used DBCC CHECKIDENT to restart Identity column count?

DBCC命令不在内部过程中工作

2 个答案: