} else {
// Target is coarser level of aggregation. Generate an aggregate.
final BitSet groupSet = new BitSet();
final IntList targetGroupList = BitSets.toList(target.getGroupSet());
for (int c : BitSets.toIter(query.getGroupSet())) {
int c2 = targetGroupList.indexOf(c);
if (c2 < 0) {
return null;
}
groupSet.set(c2);
}