Database Normalization

最新推荐文章于 2025-09-14 22:40:40 发布

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规范化是一种确保数据库设计合理，避免数据重复的过程。本文详细介绍了规范化的基本概念，包括第一范式(1NF)、第二范式(2NF)及第三范式(3NF)，并解释了如何通过分解关系来消除不必要的数据冗余，实现数据结构的良好组织。

Normalization

Defenition:Primarily a tool to validate and improve a logical design so that it satisfies certain constraints that avoid unnecessary duplication of data

simply to say ,it is just a way to process the relationship to avoid unnecessary duplication of data and produce well-structured relations.

Normalization process

first normal form

No multivalued attributes
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Second Normal form

Then we should find the primary key: Sid ,Course_id
every non-key attribute must be depedent on by the entire key,not just part of the primary key
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therefore it is not in the second normal form.
to convert this realtion into second normal form,we have to make all non-primary attributes to be fully functionally depedent on the primary key.To do that ,we need to decompose the two or more relations.
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3-NF

2NF plus no transitive depedencies (one attribute functionally determines a second,which functionally determines a third)
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when we are handling with the 2NF ,there maybe transitive depedency ,then we should make it into much smaller relation,docompose the relation,this is called the 3NF.

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