It would be good if you could post the table structures.
I think there are multiple ways of doing what you want.
a) If id is the key between the tables, you probably don't need to do anything. Your id_desc should be linked to your id, i.e. you can use in a sheet object expression as replacement to id or descriptive additional column.
b) If latter, you could also (left) join the tables.
c) You could reload your second table in a MAPPING LOAD, using only the fields giving the id and the description, and then use applymap() function to add the descriptive field to your first table or to any table that you only have the id in.
d) Use lookup() function in the first table to access the descriptive field in the second based on id, something like
LOAD
id
lookup('id_desc','id_field_in_second_table',id,'second_table_name') as id_description
...
from Table1;
