Based on those pages [1], [2], I understand that for group sets to be a
rollup, all groups in the group set must be the same as the union set of
groups but with gradually one less group removed from the end. For example,
the following are valid rollup groups (The union set of groups is *(G1, G2,
G3
The key word is "sets". I think you will agree that
((5,3), (5), ())
is a rollup. Well, it is equivalent to
((3, 5), (5), ())
because each grouping set is a SET, and therefore the order of
elements does not matter: (3, 5) is the same as (5, 3).
Now, if you're using MySQL, for instance, I c
