@Override
    public int hashCode()
    {
      final int prime = 31;
      int result = super.hashCode();
      result = prime * result + ((order == null) ? 0 : order.hashCode());
      result = prime * result + ((nullOrder == null) ? 0 : nullOrder.hashCode());
      return result;
    }
Add order expressions from the list of expressions in the format of ASTNode
@param nodes
ql/src/java/org/apache/hadoop/hive/ql/parse/PTFInvocationSpec.java