public ArrayList<String> getAllKeysInGroup(String group){
    ResultSet rs;
    try{
      String key;
      ArrayList<String> keys = new ArrayList<String>();
      
      PreparedStatement prep = this.conn.prepareStatement("SELECT key FROM keyval WHERE collection = ?");
      prep.setString(1, group);
      rs = prep.executeQuery(); 
      while(rs.next()){
        key = rs.getString(1);
        keys.add(key);
      }
      rs.close();
      return keys;
    }catch(Exception e){
      e.printStackTrace();
      return null;
    }
  }