Obtaining a natural join by specifying the common columns
SELECT * FROM IS_CALLED JOIN IS_ENROLLED_ON USING ( StudentId )
However, a named columns join doesn't always have an equivalent formulation using NATURAL JOIN. That's because although each USING column must be a common column, it is not necessary to specify all the common columns.
A common column whose name does not appear in the USING list gives rise to two columns of that name in the result, which therefore does not represent a relation. To cater for cases where the columns used for matching purposes are not common columns, and/or the matching operator is not "=", the required joining condition can be spelled out as shown in Example, in parentheses following the key word ON.