第一范式、第二范式、第三范式 第一范式 如果一个关系模式R的所有属性都是不可分的基本数据项，则R1NF（即R符合第一范式）。 两点: 一、每个字段都只能存放单一值 课程有两个值，不符合第一范式，可改为如下 二、每笔记录都要能利用一个惟一的主键来加以识别
第一范式、第二范式、第三范式
第一范式
如果一个关系模式R的所有属性都是不可分的基本数据项，则R∈1NF（即R符合第一范式）。
两点:
一、每个字段都只能存放单一值
课程有两个值，不符合第一范式，可改为如下
二、每笔记录都要能利用一个惟一的主键来加以识别
这里出现了重复组，同样不满足第一范式，因为缺乏唯一标识码,可改为
第二范式
若关系模式R∈1NF（即R符合第一范式），并且每一个非主属性都完全依赖于R的码，则R∈2NF（即R符合第二范式）。
这里表的码为(学号,课程), 即知道这两项可以确定系名、宿舍、分数，或者是这三项依赖于前两项,可知
分数完全依赖(学号,课程)系名部分依赖(学号,课程),即知道学号或者课程就能确定系名.宿舍楼部分依赖(学号,课程),即知道学号或者课程就能确定宿舍楼.
由于非主属性系名，宿舍楼不完全依赖与码，不符合第二范式，可改为
表1
第三范式
若关系模式R∈3NF（即R符合第三范式）,则每一个非主属性既不部分依赖于码也不传递依赖于码。
上面的表2不符合第三范式，这是因为你知道了系名，同样也就知道了宿舍楼，称宿舍楼传递依赖于码（学号），可分解为
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