public List getAllUsersWithReservations(int cowlab, List pers, java.util.Date start, java.util.Date end) throws SQLException {
        String periods = " AND (";
        Period p = (Period)pers.get(0);
        periods = periods + "periodid='"+p.getId()+"'";
        for(int i=1;i<pers.size();i++){
            Period p1 = (Period)pers.get(i);
            periods = periods+" or periodid='"+p1.getId()+"') ";
        }
        String query = "SELECT * FROM reservations WHERE userid <> '?' and cowlab='?' "+periods+" and date >= '?' and date '?' GROUP BY userid;";
        List ls = new ArrayList();
        PreparedStatement st = dbcon.prepareStatement(query);
        st.setInt(1,0);
        st.setInt(2,cowlab);
        st.setDate(3,new java.sql.Date(start.getTime()));
        st.setDate(4,new java.sql.Date(end.getTime()));
        ResultSet rs = st.executeQuery();
        while (rs.next()) {
            ls.add(String.valueOf(rs.getInt("userid")));
        }
        return ls;

    }