@Override
    public boolean equals(Object obj)
    {
      if (this == obj) {
        return true;
      }
      if (obj == null) {
        return false;
      }
      if (getClass() != obj.getClass()) {
        return false;
      }
      OrderSpec other = (OrderSpec) obj;
      if (expressions == null)
      {
        if (other.expressions != null) {
          return false;
        }
      }
      else if (!expressions.equals(other.expressions)) {
        return false;
      }
      return true;
    }
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