assert(plan.getChildCount() == 1);
AggregatePlanNode aggplan = (AggregatePlanNode)plan;
// handle one single min() / max() now
// TODO: combination of [min(), max(), count()]
SortDirectionType sortDirection = SortDirectionType.INVALID;
if (aggplan.isTableMin()) {
sortDirection = SortDirectionType.ASC;
} else if (aggplan.isTableMax()) {
sortDirection = SortDirectionType.DESC;