I read the spec and came away wondering how USING clause comparator
class should interact with ASC[ENDING] and DESC[ENDING] ordering that
might be introduced into ORDER ... BY ... in the future.
For instance, if we had:
C = order B by key1 ascending, key2 descending, key3;
It's clear what should happen (key3 default ordering is ascending).
But what happens if the user adds a USING clause:
C = order B by key1 ascending, key2 descending, key3 using
Are the ordering constraints from the BY clause passed to the user
defined comparator SpecialOrderClass execution function?
Is an error raised that says asc/desc ordering and using are mutually