SQL> create table widgets (product_id int, color CHAR(25));

Table created.

SQL> insert into widgets values (1, 'red');

1 row created.

SQL> insert into widgets values (2, 'blue');

1 row created.

SQL> create table sprockets (product_id int, color CHAR(25));

Table created.

SQL> insert into sprockets values (1, 'green');

1 row created.

SQL> insert into sprockets values (3, 'yellow');

1 row created.

SQL> select * from widgets w left join sprockets s on s.product_id = w.product_id;

PRODUCT_ID COLOR                     PRODUCT_ID COLOR
---------- ------------------------- ---------- -------------------------
         1 red                                1 green
         2 blue

SQL> select * from widgets w left join sprockets s on w.product_id = s.product_id;

PRODUCT_ID COLOR                     PRODUCT_ID COLOR
---------- ------------------------- ---------- -------------------------
         1 red                                1 green
         2 blue

SQL> select * from sprockets s left join widgets w on s.product_id = w.product_id;

PRODUCT_ID COLOR                     PRODUCT_ID COLOR
---------- ------------------------- ---------- -------------------------
         1 green                              1 red
         3 yellow

SQL> select * from sprockets s left join widgets w on w.product_id = s.product_id;

PRODUCT_ID COLOR                     PRODUCT_ID COLOR
---------- ------------------------- ---------- -------------------------
         1 green                              1 red
         3 yellow