returns 0 rows; however
according to the standard:
The <empty grouping set> is regarded as the shortest such initial sublist. For example, “ROLLUP ( (A, B), (C, D) )”
is equivalent to “GROUPING SETS ( (A, B, C, D), (A, B), () )”.
so I think the totals row (the grouping for () should be present) - psql returns it.