message: bug fix in cross product with more than two tables
diff: @@ -268,6 +268,7 @@ unique_ptr<TableRef> TransformFrom(List *root) {
  auto old_res = move(result);
  result = make_unique<CrossProductRef>();
  result->left = move(old_res);
  + result->right = move(next);
  cur_root = result.get();
  }
  }
  