It's not clear what is relation between caling sproc in a loop and evaluating a string. Can you provide more details?

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>Exactly, I am calling sp_executesql and one of the input parameters has to be a string, but this string is a variable expression which needs to be evaluated for the stored procedure to work fine because the stored procedure is called inside a loop.
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>@expr = '@var1 + @var2' in the first loop, and next loop it may be:
>@expr = '@var1 + @var2 + @var3 + @var4'
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>In some way, @expr is made of different variables but I need to convert it into only one: the evaluated expression.
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