Database: principles of MySQL table design - Three Paradigms

Sneak on 2021-01-21 17:48:04
database principles mysql table design


Preface

The table of relational database is designed , We often need to consider which business fields should be placed in which table , Whether the field should be split , How tables relate to each other . Is there any corresponding specification or principle to guide us to design tables ? Three paradigms for database design ; Three paradigms are mainly used to solve the relationship between tables , And field redundancy

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First normal form

  • All columns are inseparable , The goal of the first paradigm is to ensure the atomicity of each column , Each column is the smallest unit of data that cannot be further divided
  • Height and weight are two attributes , Against the first paradigm , Cannot be divided into the same column
  • Design in line with the first paradigm

Second normal form

  • First satisfy the first paradigm , And the non primary key columns in the table do not depend on the primary key or partially depend on it , Make sure that each column is related to the primary key . Generally, there are multiple primary keys , Or there is a composite primary key , Therefore, it is necessary to dismantle the meter
  • There is a composite primary key ( Student number , Discipline ), But the score of science only depends on the division - Discipline , Not in line with the second paradigm
  • The correct demonstration of the second paradigm

Third normal form

  • Satisfying the second paradigm , And the columns in the table do not have a pass through dependency on non primary key columns , Each column is directly related to the primary key column , Not indirectly
  • It's in the grade sheet , Hobbies depend on students , The students depend on the primary key again ID, In the presence of transfer dependency, the personal information of students should be extracted as a table .
  • In line with the norms of the third paradigm

Welcome refers to a mistake in the text

Reference article

  • mysql Three paradigms of database design [1]

Reference

[1]

mysql Three paradigms of database design : https://www.cnblogs.com/xiaozengzeng/p/10720226.html

This article is from WeChat official account. - Sneak forward (qianxingcsc)

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Original publication time : 2021-01-15

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