GROUP BY supports grouping by multiple elements. Alias, Field Style or with Expressions that only use one dimension, e.g. DAY ( Alias.SomeDateField ).
Group by will run faster if the cardinality of the group dimensions multiplied together are less than 500,000. This will use a Parallelizable algorithm using arrays.
Cardinality greater than this will currently use a different parallel algorithm using a dictionary, which are
slower. Cardinality of (9^10^18 ) ^ 16 is supported. This should be good for at least 32 dimensions, and many more in practice.