private void evaluateIntervalDayTime(ColumnVector colVector) {
    IntervalDayTimeColumnVector dcv = (IntervalDayTimeColumnVector) colVector;
    dcv.isRepeating = true;
    if (!isNullValue) {
      dcv.isNull[0] = false;
      dcv.set(0, intervalDayTimeValue);
    } else {
      dcv.isNull[0] = true;
      dcv.noNulls = false;
    }
  }
Constant is represented as a vector with repeating values.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/ConstantVectorExpression.java