public static String getBuiltinAggregationName(TAggregationType aggregationType) {
    if (aggregationType == null) {
      return null;
    }
    switch (aggregationType) {
      case COUNT:
        return SqlConstant.COUNT;
      case AVG:
        return SqlConstant.AVG;
      case SUM:
        return SqlConstant.SUM;
      case FIRST_VALUE:
        return SqlConstant.FIRST_VALUE;
      case LAST_VALUE:
        return SqlConstant.LAST_VALUE;
      case MAX_TIME:
        return SqlConstant.MAX_TIME;
      case MIN_TIME:
        return SqlConstant.MIN_TIME;
      case MAX_VALUE:
        return SqlConstant.MAX_VALUE;
      case MIN_VALUE:
        return SqlConstant.MIN_VALUE;
      case EXTREME:
        return SqlConstant.EXTREME;
      case COUNT_IF:
        return SqlConstant.COUNT_IF;
      case TIME_DURATION:
        return SqlConstant.TIME_DURATION;
      case MODE:
        return SqlConstant.MODE;
      case COUNT_TIME:
        return SqlConstant.COUNT_TIME;
      case STDDEV:
        return SqlConstant.STDDEV;
      case STDDEV_POP:
        return SqlConstant.STDDEV_POP;
      case STDDEV_SAMP:
        return SqlConstant.STDDEV_SAMP;
      case VARIANCE:
        return SqlConstant.VARIANCE;
      case VAR_POP:
        return SqlConstant.VAR_POP;
      case VAR_SAMP:
        return SqlConstant.VAR_SAMP;
      default:
        return null;
    }
  }
Return aggregation function name by given function type. If aggregation type is UDAF, you shall
acquire its name in other ways.

@param aggregationType aggregation type
@return the name of the aggregation or null if its aggregation type is null
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/utils/SchemaUtils.java