Is there a way to convert @my_variable string into a value of @my_variable?
I have a table which stores names of variables. I need to get the value of this variable. Something like this:
DECLARE @second_variable AS NVARCHAR(20);
DECLARE @first_variable AS NVARCHAR(20);
SET @first_variable = '20';
SET @second_variable = SELECT '@first_variable'; --here I want that @second variable be assigned a value of "20".
You can use sp_executesql to execute strings (so you could do something like sp_executesql 'SET @second_variable = ' + @name_of_variable;). However, just putting that one statement into sp_executesql won't work, since strings executed with sp_executesql or EXECUTE have their own variable scope, and, therefore, neither @second_variable nor @first_variable are accessible.
So, what you could do would be to move your complete code (excluding the name of the variable) into a sp_executesql statement (untested):
DECLARE @name_of_variable NVARCHAR(MAX)
SET @name_of_variable = ...
EXECUTE sp_executesql N'...lots of code... ' + @name_of_variable + ' ...lots of code...'
The most likely solution to your problem is to address/change/fix the design that requires why you would have a table that stores the names of variables.
try sp_executesql
declare @f nvarchar(20)
declare @s nvarchar(20)
declare @sT nvarchar(100)
set @f = '20'
set @sT = 'set @s = ''' + @f + ''''
exec sp_executesql @sT, N'@s nvarchar(20) output', @s output
print @s
'@f' (note the quotes) to 20, with the string '@f' originating from a table. In your example, you use @f explicitly, i.e., it is bound at compile time.