private boolean isReducible(final SqlKind kind) {
    if (SqlKind.AVG_AGG_FUNCTIONS.contains(kind)) {
      return true;
    }
    if (kind == SqlKind.SUM0) {
      return true;
    }
    return false;
  }
Returns whether the aggregate call is a reducible function
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveAggregateReduceFunctionsRule.java