Put value on table inside variable?

I need to put a filename that is already listed into a table. I need to put the filename to address to access the file.

I already tried this:

DECLARE @filename AS varchar(255)
DECLARE @filepath AS varchar (255)
--SELECT MAX(id) FROM ##TempFileName

SET @filename = 'SELECT tfn.subdirectory FROM ##TempFileName tfn WHERE id = ''1'''
EXEC (@filename)
--PRINT @filename 

set @filepath = 'D:romliLockAmount_out' + @filename  + '.txt'
EXEC (@filepath)
PRINT @filepath

I expect @filepath will contain something like this D:romliLockAmount_out123456.txt, how I can store the filename in a table to store in a variable?

Answer

Seeing that you want two different variables : @filename and @filepath, you can assign them on the same query.

select @filename = tfn.subdirectory,
       @filepath = 'D:romliLockAmount_out' + tfn.subdirectory + '.txt'
from ##TempFileName tfn 
where tfn.id = '1'