单属性主键和第二范式（2NF）

问题描述

我不确定此语句是对还是错：具有单个属性主键的表会自动至少采用第二范式（2NF）。

I am not sure if this statement is true or false: "A table with a single attribute primary key is automatically in at least second normal form (2NF)."

我认为这是对的，但我无法证明原因。

I think it is TRUE but I cannot justify why.

推荐答案

表要是第一个普通形式的属性一个表的值不能有多个值

For a table to be in first normal form,an attribute of a table cannot have multiple values

例如，

id   mobile_number   age
------------------------------
1    9xxx5xxxxx      25
     9xxx6xxxxx
2    8xxxx5xxxx      26
     7xxxx5xxxx

可以将其标准化为1NF，如下所示：

This can be normalized to 1NF as follows,

id  mobile_number  age
------------------------------------
1   9xxx5xxxxx     25
1   9xxx6xxxxx     25
2   8xxxx5xxxx     26
2   7xxxx5xxxx     26

如果表是第一种普通形式且没有非素数a，则该表被称为第二种普通形式属性取决于任何候选密钥的适当子集

A table is said to be in second normal form if the table is in the first normal form and no non-prime attributes depend on a proper subset of any candidate key

此处候选密钥为{id，mobile_number}

Here candidate key is {id,mobile_number}

Non主属性是年龄

该表不在2NF中，因为非主属性（age）仅取决于候选键（id）的适当子集。

The table is not in 2NF because the non-prime attribute(age) is dependent on proper subset of candidate key(id) alone.

要将其标准化为2NF，我们按如下所示拆分表

To normalize this to 2NF,we split the table as follows

id   mobile_number
------------------------------
1    9xxx5xxxxx
1    9xxx6xxxxx
2    8xxxx5xxxx
2    7xxxx5xxxx

id age
------
1  25
2  26

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