建立一个学生选课信息数据库包含关系表格、数据。数据内容s，c，sc代表学生，老师和所选课程。可以实现一般单表查询，分组、统计查询，嵌套查询和不相关子查询，集合查询，多表连接查询-Establish a relationship between student enrollment form information database contains data. Data content s, c, sc on behalf of students, teachers and selected c