外键为主键 [英] Foreign key as Primary key

问题描述

我设计了这样的表：

table1: students
---------------------
PK id
name
number
...
---------------------

table2: students_score
---------------------
PK FK student_id
math_score
english_score
...
---------------------

问题1

如果有些学生根本没有分数，好的表格设计？

If some students doesn't have scores at all, is it good table design?

问题2

如果是好的设计，那么如何在MySQL中使FK成为PK？我不知道如何。每次我尝试与上面的关系SQLYog说这个错误：无法创建表'学生＃sql-a31_2c8e'（errno：150）

If it's good design, then how can I make FK as PK in MySQL? I can't find out how. Everytime I try to make a relation like above SQLYog says this error: Can't create table 'students.#sql-a31_2c8e' (errno: 150)

谢谢

更新

发现问题2的答案 from这里。这只是一个类型（int，signed int）的问题。

I found an answer of the question 2 from here. This was just a problem of type(int, signed int).

推荐答案

我会建议更多的这些方面： p>

I would suggest something more along these lines:

table1: students
---------------------
PK id
name
number
...
---------------------

table3: classes
---------------------
pk id
name

table2: students_score
---------------------
fk student_id
fk class_id
score
PK(student_id, class_id)

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