SET IMPLICIT_TRANSACTIONS (Transact-SQL)

适用于: SQL Server(所有受支持的版本) Azure SQL 数据库 Azure SQL 托管实例 Azure Synapse Analytics Analytics Platform System (PDW)

为了连接,将 BEGIN TRANSACTION 模式设置为“隐式”。

主题链接图标Transact-SQL 语法约定

语法

SET IMPLICIT_TRANSACTIONS { ON | OFF }  

注意

若要查看 SQL Server 2014 及更早版本的 Transact-SQL 语法,请参阅早期版本文档

备注

为 ON 时,系统处于“隐式”事务模式。 这意味着如果 @@TRANCOUNT = 0,下列任一 Transact-SQL 语句都会开始新事务。 这等同于先执行一个不可见的 BEGIN TRANSACTION:

ALTER TABLE

FETCH

REVOKE

BEGIN TRANSACTION

GRANT

SELECT(参见下面的例外情况。)

CREATE

INSERT

TRUNCATE TABLE

DELETE

MERGE

UPDATE

DROP

OPEN

 

为 OFF 时,上述每个 T-SQL 语句都受一个不可见的 BEGIN TRANSACTION 和一个不可见的 COMMIT TRANSACTION 语句限制。 为 OFF 时,事务模式为自动提交。 如果 T-SQL 代码发出了一个可见 BEGIN TRANSACTION,那么事务模式为显式。

有几点需要说明:

  • 事务模式为隐式时,如果 @@trancount > 0,则不会发出不可见的 BEGIN TRANSACTION。 但是,任何显式 BEGIN TRANSACTION 语句都会递增 @@TRANCOUNT。

  • INSERT 语句和工作单元中的其他任务完成后,须发出 COMMIT TRANSACTION 语句,直到 @@TRANCOUNT 递减为 0。 也可以发出一个 ROLLBACK TRANSACTION。

  • 不会从表中选择的 SELECT 语句不会启动隐式事务。 例如,SELECT GETDATE();SELECT 1, 'ABC'; 不需要事务。

  • 由于 ANSI 默认值的原因,可能会意外打开隐式事务。 有关详细信息,请参阅 SET ANSI_DEFAULTS (Transact-SQL)

    IMPLICIT_TRANSACTIONS ON 不常用。 大多数情况下,IMPLICIT_TRANSACTIONS 为 ON,是因为选择了 SET ANSI_DEFAULTS ON。

  • 进行连接时,SQL Server Native Client OLE DB Provider for SQL Server 和 SQL Server Native Client ODBC 驱动程序会自动将 IMPLICIT_TRANSACTIONS 设置为 OFF。 对于与 SQLClient 托管提供程序进行连接,及通过 HTTP 端点接收的 SOAP 请求,SET IMPLICIT_TRANSACTIONS 默认为 OFF。

要查看 IMPLICIT_TRANSACTIONS 的当前设置,请运行以下查询。

DECLARE @IMPLICIT_TRANSACTIONS VARCHAR(3) = 'OFF';  
IF ( (2 & @@OPTIONS) = 2 ) SET @IMPLICIT_TRANSACTIONS = 'ON';  
SELECT @IMPLICIT_TRANSACTIONS AS IMPLICIT_TRANSACTIONS;  

示例

以下 Transact-SQL 脚本运行几个不同的测试用例。 还提供了文本输出,显示了每个测试用例的详细行为和结果。

-- Transact-SQL.  
-- Preparations.  
SET NOCOUNT ON;  
SET IMPLICIT_TRANSACTIONS OFF;  
GO  
WHILE (@@TranCount > 0) COMMIT TRANSACTION;  
GO  
IF (OBJECT_ID(N'dbo.t1',N'U') IS NOT NULL) DROP TABLE dbo.t1;  
GO  
CREATE table dbo.t1 (a INT);  
GO  
  
PRINT N'-------- [Test A] ---- OFF ----';  
PRINT N'[A.01] Now, SET IMPLICIT_TRANSACTIONS OFF.';  
PRINT N'[A.02] @@TranCount, at start, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
SET IMPLICIT_TRANSACTIONS OFF;  
GO 
INSERT INTO dbo.t1 VALUES (11);  
INSERT INTO dbo.t1 VALUES (12);  
PRINT N'[A.03] @@TranCount, after INSERTs, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO  
  
PRINT N' ';  
PRINT N'-------- [Test B] ---- ON ----';  
PRINT N'[B.01] Now, SET IMPLICIT_TRANSACTIONS ON.';  
PRINT N'[B.02] @@TranCount, at start, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
SET IMPLICIT_TRANSACTIONS ON;  
GO
INSERT INTO dbo.t1 VALUES (21);  
INSERT INTO dbo.t1 VALUES (22);  
PRINT N'[B.03] @@TranCount, after INSERTs, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO 
COMMIT TRANSACTION;  
PRINT N'[B.04] @@TranCount, after COMMIT, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO
  
PRINT N' ';  
PRINT N'-------- [Test C] ---- ON, then BEGIN TRAN ----';  
PRINT N'[C.01] Now, SET IMPLICIT_TRANSACTIONS ON.';  
PRINT N'[C.02] @@TranCount, at start, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
SET IMPLICIT_TRANSACTIONS ON;  
GO  
BEGIN TRANSACTION;  
INSERT INTO dbo.t1 VALUES (31);  
INSERT INTO dbo.t1 VALUES (32);  
PRINT N'[C.03] @@TranCount, after INSERTs, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO  
COMMIT TRANSACTION;  
PRINT N'[C.04] @@TranCount, after a COMMIT, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
COMMIT TRANSACTION;  
PRINT N'[C.05] @@TranCount, after another COMMIT, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO
  
PRINT N' ';  
PRINT N'-------- [Test D] ---- ON, INSERT, BEGIN TRAN, INSERT ----';  
PRINT N'[D.01] Now, SET IMPLICIT_TRANSACTIONS ON.';  
PRINT N'[D.02] @@TranCount, at start, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
SET IMPLICIT_TRANSACTIONS ON;  
GO 
INSERT INTO dbo.t1 VALUES (41);  
BEGIN TRANSACTION;  
INSERT INTO dbo.t1 VALUES (42);  
PRINT N'[D.03] @@TranCount, after INSERTs, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO 
COMMIT TRANSACTION;  
PRINT N'[D.04] @@TranCount, after a COMMIT, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
COMMIT TRANSACTION;  
PRINT N'[D.05] @@TranCount, after another COMMIT, == ' + CAST(@@TRANCOUNT AS NVARCHAR(10));  
GO
  
-- Clean up.  
SET IMPLICIT_TRANSACTIONS OFF;  
GO  
WHILE (@@TranCount > 0) COMMIT TRANSACTION;  
GO  
DROP TABLE dbo.t1;  
GO

下面是上述 Transact-SQL 脚本的文本输出。

-- Text output from Transact-SQL:  
  
-------- [Test A] ---- OFF ----  
[A.01] Now, SET IMPLICIT_TRANSACTIONS OFF.  
[A.02] @@TranCount, at start, == 0  
[A.03] @@TranCount, after INSERTs, == 0  
  
-------- [Test B] ---- ON ----  
[B.01] Now, SET IMPLICIT_TRANSACTIONS ON.  
[B.02] @@TranCount, at start, == 0  
[B.03] @@TranCount, after INSERTs, == 1  
[B.04] @@TranCount, after COMMIT, == 0  
  
-------- [Test C] ---- ON, then BEGIN TRAN ----  
[C.01] Now, SET IMPLICIT_TRANSACTIONS ON.  
[C.02] @@TranCount, at start, == 0  
[C.03] @@TranCount, after INSERTs, == 2  
[C.04] @@TranCount, after a COMMIT, == 1  
[C.05] @@TranCount, after another COMMIT, == 0  
  
-------- [Test D] ---- ON, INSERT, BEGIN TRAN, INSERT ----  
[D.01] Now, SET IMPLICIT_TRANSACTIONS ON.  
[D.02] @@TranCount, at start, == 0  
[D.03] @@TranCount, after INSERTs, == 2  
[D.04] @@TranCount, after INSERTs, == 1  
[D.05] @@TranCount, after INSERTs, == 0  

下面是结果集。

另请参阅

ALTER TABLE (Transact-SQL)
BEGIN TRANSACTION (Transact-SQL)
CREATE TABLE (Transact-SQL)
DELETE (Transact-SQL)
DROP TABLE (Transact-SQL)
FETCH (Transact-SQL)
GRANT (Transact-SQL)
INSERT (Transact-SQL)
MERGE (Transact-SQL)OPEN (Transact-SQL)
REVOKE (Transact-SQL)
SELECT (Transact-SQL)
SET 语句 (Transact-SQL)
SET ANSI_DEFAULTS (Transact-SQL)
@@TRANCOUNT (Transact-SQL)
TRUNCATE TABLE (Transact-SQL)
UPDATE (Transact-SQL)