SQL 不明白错误信息：必须声明标量变量“@Username”。
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Don't understand error message: Must declare the scalar variable "@Username".
提问by Luuk Krijnen
I have a simple script updating and showing a useraccount. (working with the management studio 2010) For preventing user errors I wanna use a variable in SQL (never did this before).
我有一个简单的脚本更新和显示用户帐户。（与 management studio 2010 合作）为了防止用户错误，我想在 SQL 中使用一个变量（以前从未这样做过）。
When reading tutorials it should be as simple as codesample below except I i'm getting an error message. Searching the web for people with the same error, I end up seeing very complex code with the same error. Can someone give me a clue.
阅读教程时，它应该像下面的代码示例一样简单，除非我收到一条错误消息。在网上搜索有相同错误的人，我最终看到非常复杂的代码有相同的错误。有人可以给我一个线索。
DECLARE @Username nvarchar(256)
Set @Username = 'theUsername'
UPDATE aspnet_Membership
SET IsLockedOut = 0
WHERE UserId IN (SELECT U.UserId
FROM aspnet_Users as U inner join aspnet_Membership M on U.UserId = M.UserId
WHERE u.UserName = @Username)
GO
SELECT U.UserId, U.UserName, M.Password, M.IsLockedOut, U.LastActivityDate
FROM aspnet_Users as U inner join aspnet_Membership M on U.UserId = M.UserId
WHERE u.UserName = @Username
Msg 137, Level 15, State 2, Line 3 Must declare the scalar variable "@Username".
消息 137，级别 15，状态 2，第 3 行 必须声明标量变量“@Username”。
回答by alexm
The scope of variable in Transact-SQL is limited by batch. Your script contains two batches separated by "GO"
Transact-SQL 中变量的范围受批处理的限制。您的脚本包含以“GO”分隔的两个批次
回答by rabudde
There is a GOinside your script, GOdivides your script into two batches so have to re-define all used variables after GO, because the scope is limited to this batch.
GO你的脚本里面有一个，GO把你的脚本分成两批，所以必须在 之后重新定义所有使用的变量GO，因为范围仅限于此批。
BTW: I don't think, that this GOis necessary, isn't it?
BTW：我不认为，这GO是必要的，不是吗？
Thanks to @gbn and @alexm giving hint, that GOseparate statements into batches and not into transactions, see also http://msdn.microsoft.com/en-us/library/ms188037.aspx
感谢@gbn 和@alexm 给出提示，GO将语句分成批次而不是事务，另见http://msdn.microsoft.com/en-us/library/ms188037.aspx
回答by ErikE
GOseparates batches and is a clientinstruction, not a serverone. So the server receives the second batch separately as a new query and in this the variable is not declared.
GO分离批次并且是客户端指令，而不是服务器指令。因此，服务器将第二批作为新查询单独接收，并且在此未声明变量。
If you try to do the following you will get an error, because the server does not understand the command GO:
如果您尝试执行以下操作，您将收到错误消息，因为服务器不理解该命令GO：
DECLARE @SQL varchar(1000);
SET @SQL = 'PRINT ''hello'';
GO
PRINT ''goodbye'';';
The server won't split this into two batches, because batches are things submitted to the server by the client.
服务器不会将其拆分为两个批次，因为批次是客户端提交给服务器的东西。
回答by Amar Palsapure
Once you write GO, @Username is not available to SELECT query.
编写 GO 后，@Username 不可用于 SELECT 查询。
回答by StaWho
you have to redefine @Usernameafter GOstatement
你必须@Username在GO声明之后重新定义
