blocks|key|1481815|text|TSQL中的Print语句是一个被误解的东西，可能是因为它的名字。它实际上向错误/消息处理机制发送一条消息，然后将其传输到调用应用程序。打印是相当愚蠢的。您只能发送8000个字符(4000个unicode字符)。您可以发送文字字符串、字符串变量(varchar或char)或字符串表达式。如果使用RAISERROR，则只能使用2,044个字符的字符串。但是，使用它向调用应用程序发送信息要容易得多，因为它调用的格式化函数类似于标准C库中的旧printf。除了文本消息之外，RAISERROR还可以指定错误号、严重性和状态代码，它还可以用于返回使用sp_addmessage系统存储过程创建的用户定义的消息。您还可以强制记录消息。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1481816|您的错误处理例程对于接收消息没有任何好处，尽管消息和错误是如此相似。当然，这种技术会根据您连接到数据库的实际方式(OLBC、OLEDB等)而有所不同。为了接收和处理来自SQL+Server数据库引擎的消息，在使用System.Data.SQLClient时，需要创建一个SqlInfoMessageEventHandler委托，标识处理事件的方法，以侦听SqlConnection类上的InfoMessage事件。您会发现，诸如严重性和状态之类的消息上下文信息被作为参数传递给回调，因为从系统的角度来看，这些消息就像是错误。|1481817|在你的应用程序中获得这些消息的方法总是一个好主意，即使你只是假脱机到一个文件，因为当你试图解决一个真正晦涩难懂的问题时，它们总是有用的。然而，我不认为我会希望最终用户看到它们，除非你能保留一个在应用程序中显示内容的信息级别。|1481818|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

The Print statement in TSQL is a misunderstood creature, probably because of its name. It actually sends a message to the error/message-handling mechanism that then transfers it to the calling application. PRINT is pretty dumb. You can only send 8000 characters (4000 unicode chars). You can send a literal string, a string variable (varchar or char) or a string expression. If you use RAISERROR, then you are limited to a string of just 2,044 characters. However, it is much easier to use it to send information to the calling application since it calls a formatting function similar to the old printf in the standard C library. RAISERROR can also specify an error number, a severity, and a state code in addition to the text message, and it can also be used to return user-defined messages created using the sp_addmessage system stored procedure. You can also force the messages to be logged.

Your error-handling routines won’t be any good for receiving messages, despite messages and errors being so similar. The technique varies, of course, according to the actual way you connect to the database (OLBC, OLEDB etc). In order to receive and deal with messages from the SQL Server Database Engine, when you’re using System.Data.SQLClient, you’ll need to create a SqlInfoMessageEventHandler delegate, identifying the method that handles the event, to listen for the InfoMessage event on the SqlConnection class. You’ll find that message-context information such as severity and state are passed as arguments to the callback, because from the system perspective, these messages are just like errors.

It is always a good idea to have a way of getting these messages in your application, even if you are just spooling to a file, because there is always going to be a use for them when you are trying to chase a really obscure problem. However, I can’t think I’d want the end users to ever see them unless you can reserve an informational level that displays stuff in the application.

blocks|key|1697076|text|对于其他阅读这个问题的人来说，如果他们的输出中确实缺少打印语句，那么实际上存在打印执行但没有返回给客户机的情况。我不能告诉你具体是什么。我可以告诉您，如果您将go语句放在任何print语句之前和之后，您将看到它是否被执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1697077|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

For the benefit of anyone else reading this question that really is missing print statements from their output, there actually are cases where the print executes but is not returned to the client. I can't tell you specifically what they are. I can tell you that if you put a go statement immediately before and after any print statement, you will see if it is executed.

blocks|key|1481945|text|查询分析器缓冲消息。PRINT和RAISERROR语句都使用此缓冲区，但RAISERROR语句具有WITH+NOWAIT选项。要立即打印消息，请使用以下命令：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1481946|RAISERROR+('Your+message',+0,+1)+WITH+NOWAIT|code-block|syntax|javascript|1481947|RAISERROR将仅显示400个字符的消息，并使用与C+printf函数类似的语法设置文本格式。|1481948|请注意，使用带有with+NOWAIT选项的RAISERROR将刷新消息缓冲区，因此还将输出所有以前缓冲的信息。|1481949|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Query Analyzer buffers messages. The PRINT and RAISERROR statements both use this buffer, but the RAISERROR statement has a WITH NOWAIT option. To print a message immediately use the following:

<pre><code>RAISERROR ('Your message', 0, 1) WITH NOWAIT
</code></pre>

RAISERROR will only display 400 characters of your message and uses a syntax similar to the C printf function for formatting text.

Please note that the use of RAISERROR with the WITH NOWAIT option will flush the message buffer, so all previously buffered information will be output also.

blocks|key|1481995|text|我最近遇到了这个问题，这是因为我在一个null变量上使用了convert语句。由于这会导致错误，因此整个print语句呈现为null，并且根本不打印。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1481996|示例-这将失败：|1481997|declare+@myID+int=null
print+'First+Statement:+'+%2B+convert(varchar(4),+@myID)|code-block|syntax|javascript|1481998|示例-这将打印：|1481999|declare+@myID+int=null
print+'Second+Statement:+'+%2B++coalesce(Convert(varchar(4),+@myID),'@myID+is+null')|1482000|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I recently ran into this, and it ended up being because I had a convert statement on a null variable. Since that was causing errors, the entire print statement was rendering as null, and not printing at all.

Example - This will fail:

<pre><code>declare @myID int=null
print 'First Statement: ' + convert(varchar(4), @myID)
</code></pre>

Example - This will print:

<pre><code>declare @myID int=null
print 'Second Statement: ' + coalesce(Convert(varchar(4), @myID),'@myID is null')
</code></pre>

blocks|key|1482076|text|您是否有与这些输出语句相关联的变量？如果是这样，我发现如果变量没有值，那么print语句将不会被输出。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1482077|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Do you have variables that are associated with these print statements been output? if so, I have found that if the variable has no value then the print statement will not be ouput.

Why does the PRINT statement in T-SQL seem to only sometimes work? What are the constraints on using it? It seems sometimes if a result set is generated, it becomes a null function, I assumed to prevent corrupting the resultset, but could it's output not go out in another result set, such as the row count?

PRINT statement in T-SQL

SQL Server

数据库

为什么T-SQL中的PRINT语句似乎只在某些时候起作用？使用它的限制是什么？似乎有时如果生成一个结果集，它会变成一个null函数，我认为这是为了防止破坏结果集，但是它的输出可以不在另一个结果集中输出吗，比如行计数？

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