因为我做的是学生成绩管理，所以数据库中至少有个一个表是来存储学生的各课成绩的。有了学生成绩，得知道这个成绩是哪个学生的，所以此表中也得有学生姓名，但是学生姓名肯定有重复的 ，所以得必须有个标志来惟一标识一个学生，所以得给每个学生一个编号（学号），但是也得必-Because I have to do is the management of student achievement, so at least there is a database a table is to store student performance in all classes. With student achievement, must know what the results are the students, so in this table have to have the students name, but the students certainly have duplicate names, so must have a unique identification mark to a student, so to each student a Number (Student ID), but also will