When we have `ORDER BY x, y` and receive input already ordered by `x`, full sort has to be done at the moment. Similarly for `GROUP BY x, y` (both cases where input is ordered by `x, y` and only by `x`).
When we have
ORDER BY x, yand receive input already ordered byx, full sort has to be done at the moment.Similarly for
GROUP BY x, y(both cases where input is ordered byx, yand only byx).