The SQL standard defines two ways to specify the join condition in an INNER JOIN or a (LEFT/RIGHT/FULL) OUTER JOIN: with an ON clause or with a USING clause. Derby currently only accepts joins with an ON clause. Internally, Derby has code that supports USING. This code should be enabled to ease the migration to Derby. We must also verify that the implementation adheres to the standard before we enable it.
Since USING is already a reserved keyword in Derby's parser, enabling the USING syntax should not cause any compatibility issues for existing queries.