SQL Inner Join and Natural Join

I'm working on an old exam paper in preparation for an exam.

Inner Join and Natural Join:

Select * From r INNER JOIN s ON r.F=s.F

Why when doing an Inner Join does 12 get removed in row E and not 20?

Select E, G From r NATURAL JOIN s;

Is 12 removed from row E and not 20?

Select * From r INNER JOIN s ON r.F=s.F

result will be

E  F  F  G
10 5  5 30
20 15 15 20

The INNER JOIN keyword selects records that have matching values in both tables. This is why 12 is removed ie, no common column. Now the result for

Select E, G From r NATURAL JOIN s

is

E  G
10 30
20 20

when you use * on select you get

F  E   G
5  10 30
15 20 20

while using * on natural join it will be expanded to the following list of columns

• All the common columns
• Every column in the first (left) table that is not a common column
• Every column in the second (right) table that is not a common column