OUTER JOIN is a subset of the ANSI/ISO SQL92 JOIN statement. It includes LEFT, RIGHT, and FULL JOIN. ANSI JOIN also includes NATURAL JOINs.

At this time, only Oracle has implemented NATURAL JOIN. Because Ingres does not support NATURAL JOIN, it is not part of OpenSQL. Until Ingres supports it, NATURAL JOIN will not be implemented in gateways.

Oracle’s OUTER JOIN syntax is similar to that of Ingres.

Because SQL Server and DB2 UDB do not support the USING clause in outer joins, USING clauses are passed through, and it is left to the underlying DBMS to determine whether the statement can be executed. If the database cannot execute the statement, it should report an error.

For more information, see "Limitations and Restrictions on OUTER JOIN and NATURAL JOIN" and "USING Clause Support" in the Ingres OpenSQL Reference Guide.