sql – difference between natural join and inner join – Stack Overflow

One significant difference between INNER JOIN and NATURAL JOIN is the number of columns returned.

Consider:

TableA                            TableB
Column1    Column2                Column1    Column3
1          2                      1          3

The INNER JOIN of TableA and TableB on Column1 will return

a.column1  a.column2  b.column1  b.column3
1          2          1          3

SELECT * FROM TableA INNER JOIN TableB USING (Column1)
SELECT * FROM TableA INNER JOIN TableB ON TableA.Column1 = TableB.Column1

The NATURAL JOIN of TableA and TableB on Column1 will return:

column1  column2  column3
1        2        3

SELECT * FROM TableA NATURAL JOIN TableB

The repeated column is avoided.

(AFAICT from the standard grammar, you can’t specify the joining columns in a natural join; the join is strictly name-based. See also Wikipedia.)

(There’s a cheat in the inner join output; the a. and b. parts would not be in the column names; you’d just have column1, column2, column1, column3 as the headings.)