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 each course and the number of students in each section, as well as the average score of each course and the number of students in each section according to the class; to query the examination results of students by the number or name of the students, and to query the students by the section of the scores.)