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
本文介绍了Candidate Key,Unique Key,Primary Key与示例之间的确切区别的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
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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