Candidate Key，Unique Key，Primary Key与示例之间的确切区别 [英] Exact difference between Candidate Key,Unique Key,Primary Key with example

问题描述

你好每一个，

i我对候选键和唯一键之间的混淆，它的使用和实现

请帮帮我!!!!









问候

Priyanka Bhagwat

hello every one,
i am getting confused between the candidate key and unique key,its use and implementation
please help me!!!!




Regards
Priyanka Bhagwat

推荐答案

阅读：候选键和主键之间的区别 [ ^ ]

候选键是列的列或列的组合，可以是表的主键。

可能有多个候选键在表格中。



任何候选键可以是主键。



唯一键是一个列，每个r都有唯一值ow，但它也允许空值（主键没有）。



任何混淆，请随时询问。



阅读 - SQL SERVER - 候选密钥和主键之间的区别 [ ^ ]

Candidate Key is a column or combination of columns, which can be a Primary key for the Table.
There may be multiple Candidate Keys In a Table.

Any Candidate Key can be a Primary Key.

Unique Key is a column which has unique value for each row, but it also allow nulls (Primary Key doesn't).

Any confusions, feel free to ask.

Read - SQL SERVER – Difference Between Candidate Keys and Primary Key[^]

候选键是a最小的（即关键，独特的关键是一个多余的关键，主键是一个废弃的概念，仍然存在于人们认为一个键可能比其他任何键更独特的日子里。



关于你的问题给出了非常好的信息此处 [ ^ ]。



-KR

Candidate key is a minimal (i.e. irreducible) key, unique key is a pleonasm, and primary key is an obsoleted concept still surviving from the days when people thought it possible for one key to be "more unique" than any of the others.

A quite excellent information is given regarding your problem here[^].

-KR

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