SQL Server 事务执行一半出错是否自动回滚整个事务

大家都知道SQL Server事务是单个的工作单元。如果某一事务成功，则在该事务中进行的所有数据修改均会提交，成为数据库中的永久组成部分。如果事务遇到错误且必须取消或回滚，则所有数据修改均被清除。

 

所以是不是说事务出错一定会回滚整个事物呢？　先看几个个例子：　

 --createtable 

create table  testrollback(idintprimarykey,
namevarchar(10))
 
 SETXACT_ABORTOFF
--Default Settings
begin tran
insert into testrollbackvalues(1,'kevin')
insert into testrollbackvalues(2,'kevin')
insert into testrollbackvalues(1,'kevin')
insert into testrollbackvalues(3,'kevin')
commit tran
 
三条成功插入只有第三条语句出错回滚
 




 
--use SETXACT_ABORT ON
SET XACT_ABORTON;
begin tran
insert into testrollbackvalues(1,'kevin')
insert into testrollbackvalues(2,'kevin')
insert into testrollbackvalues(1,'kevin')
insert into testrollbackvalues(3,'kevin')
commit tran
 
select *from testrollback
全部回滚没有数据插入
 
---use trycatch to catch error and rollback whole transcation
begin tran
    begin
try
       insert
into testrollback values (1,'kevin')
       insert
into testrollback values (2,'kevin')
       insert
into testrollback values (1,'kevin')
       insert
into testrollback values (3,'kevin')
    commit
tran
    end
try
begin catch
   rollback
end catch

 
全部回滚没有数据插入
 
对于上面的测试可以看到默认情况下SQL Server只是Rollback出错的语句而不是整个事物。所以如果想Rollback整个事物的话可以通过SET
XACT_ABORT选项设置或者使用Try Catch之类的捕获错误进行Rollback.
对于出现网络问题会跟上面的结果有点不一样。在执行事务的过程中，如果Client断开，那么SQL Server会自动Rollback整个事物。
在SSMS客户端执行第一条语句，去掉commitTran
 SET XACT_ABORTOFF--Default Settings
begin tran
insert into testrollbackvalues(1,'kevin')
insert into testrollbackvalues(2,'kevin')
insert into testrollbackvalues(1,'kevin')
insert into testrollbackvalues(3,'kevin')
 

之后断开连接，在服务器上用DBCC OPENTRAN查看open的事务：



间隔一段时间再执行发现DBCC OPENTRAN已经没有了，而且查询表数据也没有，说明整个事物回滚了。所以在客户端断开且事务没有完成的情况下整个事物回滚。
 
对于上面的测试微软有详细的解释：
If an error prevents the successful completion of a transaction, SQLServer automatically rolls back the transaction and frees all resources held bythe transaction. If the client's network connection to an instance of theDatabase Engine is broken,
any outstanding transactions for the connection arerolled back when the network notifies the instance of the break. If the clientapplication fails or if the client computer goes down or is restarted, thisalso breaks the connection, and the instance of the
Database Engine rolls backany outstanding connections when the network notifies it of the break. If theclient logs off the application, any outstanding transactions are rolled back.
If a run-time statement error (such as a constraint violation) occurs in abatch, the default behavior in the Database Engine is to roll back only thestatement that generated the error. You can change this behavior using the SETXACT_ABORT statement.
After SET XACT_ABORT ON is executed, any run-timestatement error causes an automatic rollback of the current transaction.Compile errors, such as syntax errors, are not affected by SET XACT_ABORT. Formore information, seeSET
XACT_ABORT (Transact-SQL)
更多信息参考　ControllingTransactions