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Dynamic-SQL Truncation Issue

    Question

  • I know that a similar thread exists here under a similar title ..

    But since I couldnt get much of a conclusion from it, posting here..

    The issue is that I'm building up a dynamic query - storing it into a variable of type nvarchar(max). But after a certain limit(probably after a length of 4000 - a guess) the variable seems to truncate the remaining part of the query and thereby the execution of the query throws up an error.

    There IS a workaround fr this by splitting up my query into two(multiple) variables - concatenating them and executing -yes, I know this and have done this in the past when I encountered this situation. But this time I made up my mind that I SHUD clarify this issue once and for all and hence posting it here ..

    Would be great if someone could clarify on this ..


    Thanks,
    JK

    <Please mark as 'answered' if this answers your query> <Please mark as 'helpful' if this was helpful to your query>

    Wednesday, November 06, 2013 7:54 AM

Answers

  • You may execute an  nvarchar(max) variable of any length.  But you must be careful how you build that string.  For example, the following will not work

    Declare @TestFail nvarchar(max);
    Set @TestFail = Replicate(' ', 3999) + N'Select Count(*) From sys.objects';
    Exec (@TestFail);

    The replicate value is 3,999 characters and the other constant is 32 characters, so the concatenated value would be 4031 characters which would easily fit into an nvarchar(max).  But the problem is the Replicate returns a char(3999) and the N'...' string constant returns a nchar(32).  Neither of these is an nvarchar(max).  So when you concatenate them the Replicate is converted to an nchar(3999) and SQL concatenates them, but it's not a nvarchar(max), instead it is an nchar(somenumber) or nvarchar(somenumber).  But the largest that somenumber can be is 4000, so the intermediate result of the concatenation is only 4000 characters long.  (So it has 3,999 spaces followed by an 'S').  Putting that value in @TestFail converts it to a nvarchar(max) but it is still only 4000 characters long because the rest of the string is already gone.

    The solution is to cast enough of the input values to nvarchar(max) so that every intermediate result is nvarchar(max).  The safe thing is to cast every input to nvarchar(max).  However you can get away with casting only evenough to ensure that every intermediate value must be nvarchar(max).  So the following works

    Declare @TestSuceed nvarchar(max);
    Set @TestSuceed = Cast(Replicate(' ', 3999) As varchar(max)) + N'Select Count(*) From sys.objects';
    Exec (@TestSuceed);

    It works because the replicate now produces nvarchar(max), so when it concatenates the nchar string the output is still nvarchar(max). so it keeps all 4,031 characters and the EXEC will now work correctly.

    Tom

    Wednesday, November 06, 2013 5:44 PM

All replies

  • The max size for a column of type NVARCHAR(MAX) is 2 GByte of storage.
    Since NVARCHAR uses 2 bytes per character, that's approx. 1 billion characters.

    Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/

    MS SQL optimization: MS SQL Development and Optimization
    MS SQL Consulting: Large scale of database and data cleansing
    Remote DBA Services: Improves MS SQL Database Performance
    SQL Server Integration Services: Business Intelligence

    Wednesday, November 06, 2013 8:05 AM
    Answerer
  • Hi JK,

    You can have 2 variables to store the whole script, like what you did in the past.


    Many Thanks & Best Regards, Hua Min

    Wednesday, November 06, 2013 8:33 AM
  • Hi,

    If you could post a sample of your code, that would help us diagnose the problem for you.


    Thanks, Andrew
    My blog...

    Wednesday, November 06, 2013 8:33 AM
  • As such there is no limit, except the data type length limit.

    The limit is with PRINT when using in SSMS.

    Check this where the dynamic query can accept more than 8000 characters.

    declare @test nvarchar(max)
    
    set @test='select  ''                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      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    select LEN(@test),@test
    exec(@test)


    Please use Marked as Answer if my post solved your problem and use Vote As Helpful if a post was useful.

    Wednesday, November 06, 2013 1:16 PM
  • The issue is that I'm building up a dynamic query - storing it into a variable of type nvarchar(max). But after a certain limit(probably after a length of 4000 - a guess) the variable seems to truncate the remaining part of the query and thereby the execution of the query throws up an error.

    The problem likely isn't due to truncation but rather a bug in the code.  If you need help with troubleshooting, please post the code as Andrew suggested.


    Dan Guzman, SQL Server MVP, http://www.dbdelta.com

    Wednesday, November 06, 2013 1:25 PM
  • Please post the results of SELECT @@VERSION.

    How are you executing the query, EXEC(@sql) or sp_executesql(@sql)?  What is the error?

    The problem with text that large, is SSMS has a hard time displaying it entirely. 

    Wednesday, November 06, 2013 1:31 PM
    Moderator
  • You may execute an  nvarchar(max) variable of any length.  But you must be careful how you build that string.  For example, the following will not work

    Declare @TestFail nvarchar(max);
    Set @TestFail = Replicate(' ', 3999) + N'Select Count(*) From sys.objects';
    Exec (@TestFail);

    The replicate value is 3,999 characters and the other constant is 32 characters, so the concatenated value would be 4031 characters which would easily fit into an nvarchar(max).  But the problem is the Replicate returns a char(3999) and the N'...' string constant returns a nchar(32).  Neither of these is an nvarchar(max).  So when you concatenate them the Replicate is converted to an nchar(3999) and SQL concatenates them, but it's not a nvarchar(max), instead it is an nchar(somenumber) or nvarchar(somenumber).  But the largest that somenumber can be is 4000, so the intermediate result of the concatenation is only 4000 characters long.  (So it has 3,999 spaces followed by an 'S').  Putting that value in @TestFail converts it to a nvarchar(max) but it is still only 4000 characters long because the rest of the string is already gone.

    The solution is to cast enough of the input values to nvarchar(max) so that every intermediate result is nvarchar(max).  The safe thing is to cast every input to nvarchar(max).  However you can get away with casting only evenough to ensure that every intermediate value must be nvarchar(max).  So the following works

    Declare @TestSuceed nvarchar(max);
    Set @TestSuceed = Cast(Replicate(' ', 3999) As varchar(max)) + N'Select Count(*) From sys.objects';
    Exec (@TestSuceed);

    It works because the replicate now produces nvarchar(max), so when it concatenates the nchar string the output is still nvarchar(max). so it keeps all 4,031 characters and the EXEC will now work correctly.

    Tom

    Wednesday, November 06, 2013 5:44 PM