Shows differences in table structures

select
        a.column_name, a.data_type, a.data_length, a.data_scale,a.data_precision,
        b.column_name, b.data_type, b.data_length, b.data_scale,b.data_precision
from 
        user_tab_columns a, user_tab_columns b
where
        a.table_name  = upper('&table1')  and
        b.table_name  = upper('&table2')  and
        a.column_name = b.column_name     and
        (
          a.data_type      <> b.data_type   or
          a.data_length    <> b.data_length or
          a.data_scale     <> b.data_scale  or
          a.data_precision <> b.data_precision
        );