Specifies the columns on which the join is based. Column names
    must be defined in both table references specified in the
    qualified join. The USING clause implies an equijoin condition
    between columns of the same name and creates a common column in
    the result.

    SQL> SELECT *
    cont> FROM TABLE1 LEFT OUTER JOIN TABLE2
    cont> USING (C1);
              C1     TABLE1.C2   TABLE2.C4
              10            15          AA
              20            25          CC
              30            35        NULL
    3 rows selected

    The common columns are coalesced into a single column in the
    result in the previous example. Therefore, such columns cannot be
    qualified. You can reference the coalesced column in a query. For
    example:

    SQL> SELECT *
    cont> FROM TABLE1 LEFT OUTER JOIN TABLE2
    cont> USING (C1)
    cont> WHERE C1 BETWEEN 20 AND 30;
              C1     TABLE1.C2   TABLE2.C4
              20            25          CC
              30            35        NULL
    2 rows selected