message: Fix nested subqueries with unions
diff: @@ -68,7 +68,7 @@ unique_ptr<SQLStatement> Binder::Visit(SelectStatement &statement) {
  for (size_t i = 0; i < statement.setop_left->select_list.size(); i++) {
  auto expr = make_unique<ColumnRefExpression>(
  statement.setop_left->select_list[i]->return_type, i);
  - expr->alias = statement.setop_left->select_list[i]->alias;
  + expr->alias = statement.setop_left->select_list[i]->GetName();
  new_select_list.push_back(move(expr));
  }
  }
  