try to re-use columns from the child select list

  if (node->getType() == ASTNode::T_COLUMN_NAME) {

    auto col_index = -1;

    /* check if this columns is already in the select list */

    /* check if this column already exists in the select list */

    const auto& candidates = target_select_list->getChildren();

    for (int i = 0; i < candidates.size(); ++i) {

      // FIXPAUL

      candidates[i]->debugPrint(4);

      if (candidates[i]->getType() == ASTNode::T_DERIVED_COLUMN) {

        if (candidates[i]->getChildren().size() == 1) {

          auto colname = candidates[i]->getChildren()[0];

          if (colname->getType() == ASTNode::T_COLUMN_NAME &&

              node->getToken()->getString() ==

                  colname->getToken()->getString()) {

            col_index = i;

            break;

          }

        }

      }

    }

    /* otherwise add this column to the select list */