When table's has more than one common column:
t1: col_a, col_c, col_d
t2: col_a, col_b, col_c
then does the natural join produce this? :
select * from t1 join t2 on t1.col_a = t2.col a
AND t2.colc= t1.colc
in other words combination of both a and c on the left match a and c on the right?