数据库管理系统 [英] DATABASE MANAGEMENT SYSTEM

问题描述

钥匙和超级钥匙有什么区别..我听说两者都是一样的......如果是这样的话为什么他们会给两个名字，就像一个男孩有两个名字chintoo和pappu类型

解决方案

嗯，你的问题很模糊，因为如果你谈论超级密钥，你不能只告诉密钥：有关键候选人，主键，外键等等......是一个涉及关系模型理论的所有教程都要解决的主题。你需要一定程度的线性代数理论来理解关系代数，并真正看到分数。

你试图找到什么答案？哦......你在这里发了一个问题。但是以谷歌为例呢？哦，顺便说一句，维基百科在这个主题的文章非常好：

http：// en。 wikipedia.org/wiki/Superkey [ ^ ]。 ..并且不要忘记按照参见部分中的链接。

但这也很不错：

引用：

超级键是一组唯一标识表中每一行的列，而键是这类列的最小集合。

请参阅： http://my.safaribooksonline.com/book/databases/9788131700785/3dot6-keys/ navpoint107 [ ^ ]

what is the Difference between key and super key .. i heared that both are same .. if so then why they are given two names like one boy have two name chintoo and pappu types

解决方案

Well, your question is quite vague, since if you speak about superkey, you can't just tell "key": there are key candidates, primary keys, foreign keys and so on... This is a topic that is addressed by all tutorials dealing with the relational model theory. You will need some level of linear algebra theory to understand relational algebra, and to really see the points.
What have you tried to find the answer? Oh... you posted a question here. But what about using google for example? And oh, by the way, wikipedia's article in this topic is quite good:
http://en.wikipedia.org/wiki/Superkey[^]... and don't forget to follow the links in the See also section.
But this is also quite good:

Quote:

A superkey is a set of columns that uniquely identifies every row in a table, while a key is a minimal set of such columns.

See: http://my.safaribooksonline.com/book/databases/9788131700785/3dot6-keys/navpoint107[^]

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