public static int addScore(Score s, Statement stmt) throws Exception{
		// 首先查找s对应学号的学生是否存在，如果不存在则返回-1
		// 如果学生存在，再查找该学号是否已经录入成绩
		// 如果已经录入成绩，则返回失败，否则在Score表中添加成绩
		String sel_str = "select * from stu_info where stu_no = '" + s.stu_no + "'";
		// // System.out.println(sel_str);
		if( !stmt.executeQuery(sel_str).next() ){
			return -1;
		}
		
		sel_str = "select * from score_info where stu_no = '" + s.stu_no + "'";
		// System.out.println(sel_str);
		if( stmt.executeQuery(sel_str).next() ){
			return -1;
		}
		
		String update_str = "insert into score_info values('" + s.stu_no + "',"
			+ s.chinese_score + "," + s.math_score + "," + s.english_score + ","
			+ s.computer_score + "," + s.politic_score+")";
		// System.out.println(update_str);
		if( stmt.executeUpdate(update_str) > 0 ){
			return 0;
		}
		return -1;
	}