SQL Server 异常处理机制(Begin try Begin Catch)

begin try--SQL end try begin catch --sql (处理出错动作)end catch

我们将可能会出错的sql 写在begin try...end try 之间，若出错，刚程序就跳到紧接着的begin try...end try 的beign catch...end catch中，执行beign catch...end catch错误处理SQL。try..catch 是可以嵌套的。在begin catch ...end catch中我们可以利用系统提供的下面四个函数得到出错信息：
error_number 返回错误代码
error_serverity 返回错误的严重级别
error_state 返回错误状态代码
error_message 返回完整的错误信息
上面的四个函数在同一个begin catch ...end catch可以在多次使用，值是不变的。

下面是一个简单的小例子。

begin tryselect 2/0end trybegin catchselect error_number() as error_number ,error_message() as error_message,error_state() as error_state,error_severity() as error_severityend catch

结果：
-----
error_number error_message error_state error_severity
8134 遇到以零作除数错误。 1 16
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不受 TRY…CATCH 构造影响的错误 
TRY…CATCH 构造在下列情况下不捕获错误： 
严重级别为 10 或更低的警告或信息性消息。 
严重级别为 20 或更高且终止会话的 SQL Server 数据库引擎任务处理的错误。 如果所发生错误的严重级别为 20 或更高，而数据库连接未中断，则 TRY…CATCH 将处理该错误。 
需要关注的消息，如客户端中断请求或客户端连接中断。 
当系统管理员使用 KILL 语句终止会话时。

USE AdventureWorks;GOBEGIN TRY    -- Generate a divide-by-zero error.    SELECT 1/0;END TRYBEGIN CATCH    SELECT        ERROR_NUMBER() AS ErrorNumber,        ERROR_SEVERITY() AS ErrorSeverity,        ERROR_STATE() AS ErrorState,        ERROR_PROCEDURE() AS ErrorProcedure,        ERROR_LINE() AS ErrorLine,        ERROR_MESSAGE() AS ErrorMessage;END CATCH;GO 

USE AdventureWorks;GOBEGIN TRANSACTION;BEGIN TRY    -- Generate a constraint violation error.    DELETE FROM Production.Product        WHERE ProductID = 980;END TRYBEGIN CATCH    SELECT         ERROR_NUMBER() AS ErrorNumber,        ERROR_SEVERITY() AS ErrorSeverity,        ERROR_STATE() as ErrorState,        ERROR_PROCEDURE() as ErrorProcedure,        ERROR_LINE() as ErrorLine,        ERROR_MESSAGE() as ErrorMessage;    IF @@TRANCOUNT > 0        ROLLBACK TRANSACTION;END CATCH;IF @@TRANCOUNT > 0    COMMIT TRANSACTION;GO