@Override
  public boolean isSame(Object o) {
    if (o instanceof ExprNodeDynamicValueDesc) {
      Object otherValue = ((ExprNodeDynamicValueDesc) o).getDynamicValue();
      if (dynamicValue == null) {
        return otherValue == null;
      }
      return dynamicValue.equals(otherValue);
    }
    return false;
  }
This expression represents a value that will be available at runtime.
ql/src/java/org/apache/hadoop/hive/ql/plan/ExprNodeDynamicValueDesc.java