select * 
  from table2
except
select * 
  from (select * 
           from table1
          union 
          select * 
            from table3) as ExTables

select column_name + ','
from information_schema.columns
where table_name = ' '
order by ordinal_position

remove any columns you don't want to compare and then build the query:
select col1, col2, col3...col99
from postchange_table
EXCEPT
select col1, col2, col3...col99
from prechange_table