private static List<String> parseSqls(List<Sql> sqls, boolean undo) {
    List<String> result = new ArrayList<String>();
    for (Sql sql : sqls) {
      result.add(undo? sql.getUndoSql():sql.getDoSql());
    }
    if (undo) {
      Collections.reverse(result);
    }
    return result;
  }