There needs to be a new join predicate structure to replace usingPredicate that describes a join using an equality relation between columns on the left and right. The new predicate, let's call this the equalityPredicate extends usingPredicate by allowing the names of the join columns on the left and right to differ.

Once this predicate exists, the following needs to happen:

1. the constructor for USING must be changed to use equalityPredicate
2. after sql: add hash join algorithm for USING/NATURAL predicates #10618 is merged, the hash join must be used for equalityPredicate as well.

for the purpose of EXPLAIN we can then describe the equalityPredicate using the following syntax: ON EQUALS(left columns..., right columns...)