2021/11/27大数据1+XJava答案

2021/11/27

//已经提供Student类的属性，补充完成该类的有参（五个参数）及无参构造方法
	public Student(){}
	public Student(String name,String pwd,int age,int grade,int rate){
		this.name=name;
		this.pwd=pwd;
		this.age=age;
		this.grade=grade;
		this.rate=rate;
	}

//请修改该方法，并且在赋值时，课程难度只能为：高、中、低这三种之一，其余值不做任何处理。
	public void setDifficulty(String difficulty) {
		switch(difficulty){
			case "高":this.difficulty = difficulty;break;
			case "中":this.difficulty = difficulty;break;
			case "低":this.difficulty = difficulty;break;
			default :break;
		}
		
	}

//请修改该方法，以保证打印对象时输出格式如下：(sname=zs;cname=语文;score=80)
	@Override
	public String toString() {
		return "(sname="+sname+";cname="+cname+";score="+score+")";
	}

	public int add(Student s) {
                // 请补全sql语句
                String sql = "insert into `student` values (?,?,?,?,?)";
                return studentUtil.add(sql, s.getName(),s.getPwd(),s.getAge(),s.getGrade(),s.getRate());
        }

	public int queryNum() {
                String sql = "select * from student";
                List list = studentUtil.getList(sql, Student.class);
                // 请修改以下代码，保证返回值为总人数，假设所有学生名字都不一样
                int num = list.size();
                return num;
        }

	public String queryMinAge() {
                // 请补全sql语句
                String sql = "select `name` from `student` where age = (select min(age) from `student`)";
                Student g = studentUtil.getOne(sql, Student.class);
                return g.getName();
        }

	public Course queryCourse(String name) {
                // 请补全sql语句
                String sql = "select * from `course` where `name` = ?";
                return courseUtil.getOne(sql, Course.class, name);
        }

	public boolean updateDifficultyByName(String name,String difficulty){
                // 请补全sql语句
                String sql = "update `course` set `difficulty` = ? where `name` = ?";
                int a = courseUtil.update(sql, difficulty, name);
                if(a>0){
                        return true;
                }else{
                        return false;  
                }
        }

	public String queryAvgMax() {
                // 请补全sql语句   select `sname` from (select `sname`,avg(`score`) as aa from `score` group by `sname`)tab1 where aa = (select max(aa) from (select `sname`,avg(`score`) as aa from `score` group by `sname`)tab1)
                //select max(aa) from (select `sname`,avg(`score`) as aa from `score` group by `sname`)tab1
                String sql = "select `sname` from (select `sname`,avg(`score`) as aa from `score` group by `sname`)tab1 where aa = (select max(aa) from (select `sname`,avg(`score`) as aa from `score` group by `sname`)tab1)";
                Score s = scoreUtil.getOne(sql, Score.class);
                return s.getSname();
        }

// 把集合 li 中的每个成绩对象的名字取出来放进集合 s 中,并返回
                // 请补全以下代码
                for (int i = 0; i < li.size(); i++) {     
                        s.add(li.get(i).getSname());
                }
                
                return s;