编写程序实现简单成绩管理。所有数据存储在数据库中；要求能够统计每门课程的平均分及各分数段的人数，也能按班级统计每门课的平均分及各分数段的人数；能够按学号或姓名查询学生考试成绩，也能按分数段查询学生。(Write a program to achieve simple performance management. All data are stored in the database; it is required to be able to count the average score of