Julian> I don’t think the [] means “no collation”. It means “order by zero columns”. The list of columns is present, but it is empty.
I agree I might be wrong from technical point of view. Frankly speaking, I don't think I've ever understood what Calcite traits are even though I happen to land a couple of fixes there. However I believe that the distinction is not important for the discussion. The case is planner puts known to have multiple collations relation (e.g. values, merge join) into "unknown collation" subset which erases important information. Vladimir
