Dynamic SQL Error

ScuzzyJo
ScuzzyJo used Ask the Experts™
on
Hi

I'm pretty new to using dynamic SQL and have the following bit of code:

SET @maxcounter = 0;
--
WHILE @maxcounter < @maxcnt
BEGIN
      SET @crtcnt = @maxcounter + 1;
      SET @maxcounter = @maxcounter + 1;
      SET @sqlstr = 'UPDATE LFRD SET  old_ssn' + @crtcnt + ' = substring(ConcatF,13*' + @maxcounter + ',13) WHERE old_ssn Is Not Null OR @maxcounter < SSNCount;'
      EXEC (@sqlstr);
      
END

The variables are declared and used earlier, so I'm pretty sure that isn't the problem.

I'm getting the error message:

Msg 245, Level 16, State 1, Line 137
Conversion failed when converting the nvarchar value 'UPDATE LFRD SET  old_ssn1 = substring(ConcatF,13*' to data type int.

Which refers to the @sqlstr =  line.

I'm pretty sure it's my syntax, but I don't understand why it's trying to convert to a data type int.

The line is supposed to fill various columns (the number is dynamic) with data from a concatenated column.  Each block of data is 13 characters long.  I'm trying to say that if @maxcounter is 1, start at character 13 (probably needs to be 14, but I can deal with that later) and pick up 13 characters.  If @maxcounter is 2, start at character 26 (or maybe 27) and pick up 13 characters, and so on.

Can anybody please help me here?  I don't know where I'm going wrong.

Thanks
Sarah
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Pawan KumarDatabase Expert
Awarded 2016
Top Expert 2016

Commented:
Please try this

--

SET @maxcounter = 0;
--
WHILE @maxcounter < @maxcnt 
BEGIN
      SET @crtcnt = @maxcounter + 1;
      SET @maxcounter = @maxcounter + 1;
      SET @sqlstr = 'UPDATE LFRD SET old_ssn' + @crtcnt + ' = substring( Concat(F,13) *' + @maxcounter + ',13) WHERE old_ssn Is Not Null OR @maxcounter < SSNCount;'
      EXEC (@sqlstr);
      
END

--

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IT Engineer
Distinguished Expert 2017
Commented:
@crtcnt and @maxcounter are both INT and you want to concatenate with a string and that's why you're having the error.
Use CAST function to explicitly convert it to varchar.
Also, inside the dynamic SQL your variables aren't known so you need to do the same for the WHERE clause:

SET @sqlstr = 'UPDATE LFRD SET  old_ssn' + CAST(@crtcnt AS VARCHAR) + ' = substring(ConcatF,13*' + CAST(@maxcounter AS VARCHAR)+ ',13) WHERE old_ssn Is Not Null OR ' + CAST(@maxcounter AS VARCHAR) + '< SSNCount;'
Pawan KumarDatabase Expert
Awarded 2016
Top Expert 2016
Commented:
Try this ..

--

--

SET @maxcounter = 0;
--
WHILE @maxcounter < @maxcnt 
BEGIN
      SET @crtcnt = @maxcounter + 1;
      SET @maxcounter = @maxcounter + 1;
      SET @sqlstr = 'UPDATE LFRD SET old_ssn' + CAST(@crtcnt AS VARCHAR(50)) + ' = substring(ConcatF,13*' + CAST(@maxcounter AS VARCHAR(50)) + ',13) WHERE old_ssn Is Not Null OR @maxcounter < SSNCount'
      EXEC (@sqlstr);
      
END

--

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--

Author

Commented:
Hi

Vitor - that works perfectly, thank you.  I'm going to award you the bulk of the points.

Pawan - yours was nearly there, so I'm going to award you some points.

Hope that's OK with both of you.

Thanks
Sarah

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