presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/PushPartialAggregationThroughJoin.java/PushPartialAggregationThroughJoin/pushPartialToLeftChild
class PushPartialAggregationThroughJoin:    private PlanNode pushPartialToLeftChild(AggregationNode node, JoinNode child, Context context)
    {
        Set<Symbol> joinLeftChildSymbols = ImmutableSet.copyOf(child.getLeft().getOutputSymbols());
        List<Symbol> groupingSet = getPushedDownGroupingSet(node, joinLeftChildSymbols, intersection(getJoinRequiredSymbols(child), joinLeftChildSymbols));
        AggregationNode pushedAggregation = replaceAggregationSource(node, child.getLeft(), groupingSet);
        return pushPartialToJoin(node, child, pushedAggregation, child.getRight(), context);
    }