当前位置:网站首页>[three paradigms of database] you can understand it at a glance
[three paradigms of database] you can understand it at a glance
2022-07-06 13:53:00 【No baldness】
Three paradigms
First normal form (1NF)
Make sure the database The atomicity of a field ( That is, indivisibility );
* example : Judge whether the following table conforms to First normal form ?
Number | full name | Telephone |
1 | Xue Baochai | 10076 |
2 | Jia Baoyu | 10086 |
3 | Lin daiyu | 10096 |
First of all, we need to Business needs To judge Atomic properties of fields , The only thing that can be split in the above table is the name , If the business thinks that the name is a field , Then the table satisfies the first normal form ; But if the business requires our name to be written in two fields ( Last name and first name ), It does not satisfy the first paradigm , Split the name to meet ( Here's the picture ).
Number | surname | name | Telephone |
1 | Xue | Bao Chai | 10076 |
2 | Jia | The treasure jade | 10086 |
3 | Lin | Daiyu | 10096 |
Second normal form (2NF)
In the meet 1NF On the basis of , It also contains two contents :
(1) The watch must have A primary key
(2) Non primary key columns must Completely dependent on Primary key , You can't rely on only part of the primary key ( Not partially dependent );
* example : Judge whether the following table conforms to Second normal form ?( Set up : The business requirements of this table meet the first paradigm )
full name | Gender | Telephone | Department name | Department floor |
Xue Baochai | Woman | 10076 | Public relations | 5 layer |
Jia Baoyu | male | 10086 | Publicity Department | 3 layer |
Lin daiyu | Woman | 10096 | Public relations | 5 layer |
First, on the basis of the first paradigm , We can see that the primary key of this table is Composite primary key .( full name + Department name ), Content satisfied (1) The watch must have A primary key
secondly , We found that non primary key columns are partially dependent on primary keys Instead of relying entirely on primary keys : Gender of non primary key column 、 The phone depends on the name , The non primary key column Department floor depends on the Department name
Not satisfied with the content (2) Non primary key columns must Completely dependent on Primary key , You can't rely on only part of the primary key
In order to conform to the second paradigm , We will proceed with the table Split and optimize
Job number | full name | Gender | Telephone |
101 | Xue Baochai | Woman | 10076 |
102 | Jia Baoyu | male | 10086 |
103 | Lin daiyu | Woman | 10096 |
Department number | Department name | Department floor |
1 | Public relations | 5 layer |
2 | Publicity Department | 3 layer |
1 | Public relations | 5 layer |
Department number | Job number | full name | Gender | Telephone |
1 | 101 | Xue Baochai | Woman | 10076 |
2 | 102 | Jia Baoyu | male | 10086 |
1 | 103 | Lin daiyu | Woman | 10096 |
We put Set the department number as the primary key of the Department table ( The foreign key of the master table )、 The job number is set as the primary key of the master table , Because they have no practical business significance , So when we modify the data ( For example, change your name 、 Department name ), You don't have to change it line by line .
Third normal form (3NF)
In the meet 2NF On the basis of , In addition, non primary key columns must Directly dependent on Primary key ( Cannot rely on non primary keys ), There can be no delivery dependency ,
That is, it cannot exist A Depend on B,B Depend on C;
( among A、B Is a non primary key column ,C Primary key )
* example : Judge whether the following table conforms to Third normal form ?( The business requirements of this table have met the second paradigm )
Department number | Job number | full name | Gender | Telephone | Position | Wages |
1 | 101 | Xue Baochai | Woman | 10076 | formal | 8000 |
2 | 102 | Jia Baoyu | male | 10086 | Internship | 4000 |
1 | 103 | Lin daiyu | Woman | 10096 | formal | 8000 |
In order to conform to the third paradigm , We will proceed with the table Split and optimize
First, on the basis of the first paradigm , We can see that the salary in the non primary key column of the table depends on the position in the non primary key column , There are transitive dependencies , That is, it does not meet the requirements of the third paradigm
Job number | full name | Gender | Telephone |
101 | Xue Baochai | Woman | 10076 |
102 | Jia Baoyu | male | 10086 |
103 | Lin daiyu | Woman | 10096 |
Department number | Department name | Department floor |
1 | Public relations | 5 layer |
2 | Publicity Department | 3 layer |
1 | Public relations | 5 layer |
Job number | Position | Wages |
01 | formal | 8000 |
02 | Internship | 4000 |
01 | formal | 8000 |
Department number | Job number | full name | Gender | Telephone | Job number |
1 | 101 | Xue Baochai | Woman | 10076 | 01 |
2 | 102 | Jia Baoyu | male | 10086 | 02 |
1 | 103 | Lin daiyu | Woman | 10096 | 01 |
For explanation, please refer to the end of the second paradigm
ps: We must start from the business needs ( That's the scene ) Set out to judge whether it conforms to the paradigm
Why learn paradigm ?
When we communicate business needs with customers Or is it To complete a project , We need to design a suitable data model . here , The importance of standardized design is highlighted .
What is the paradigm ?
A paradigm is a collection of relational patterns that conform to a certain level . The construction of database must follow certain rules ( In a relational database , This rule refers to the paradigm )). The relationship in relational database must meet certain requirements , That is to meet different paradigms .
What problems can learning paradigm solve ?
Learning standardized design can solve the following problems :
1. data redundancy
2. Abnormal problems :
Update exception
Insertion exception
Delete exception
边栏推荐
- The latest tank battle 2022 full development notes-1
- Inaki Ading
- MySQL中count(*)的实现方式
- 强化学习基础记录
- 7-6 矩阵的局部极小值(PTA程序设计)
- [au cours de l'entrevue] - Comment expliquer le mécanisme de transmission fiable de TCP
- 深度强化文献阅读系列(一):Courier routing and assignment for food delivery service using reinforcement learning
- 实验七 常用类的使用(修正帖)
- Brief introduction to XHR - basic use of XHR
- Package bedding of components
猜你喜欢
9. Pointer (upper)
[面试时]——我如何讲清楚TCP实现可靠传输的机制
Difference and understanding between detected and non detected anomalies
MySQL lock summary (comprehensive and concise + graphic explanation)
Callback function ----------- callback
[au cours de l'entrevue] - Comment expliquer le mécanisme de transmission fiable de TCP
SRC mining ideas and methods
(original) make an electronic clock with LCD1602 display to display the current time on the LCD. The display format is "hour: minute: Second: second". There are four function keys K1 ~ K4, and the fun
[hand tearing code] single case mode and producer / consumer mode
Nuxtjs quick start (nuxt2)
随机推荐
仿牛客技术博客项目常见问题及解答(一)
[the Nine Yang Manual] 2018 Fudan University Applied Statistics real problem + analysis
仿牛客技术博客项目常见问题及解答(三)
C language Getting Started Guide
[the Nine Yang Manual] 2016 Fudan University Applied Statistics real problem + analysis
FAQs and answers to the imitation Niuke technology blog project (II)
7-8 7104 约瑟夫问题(PTA程序设计)
JS several ways to judge whether an object is an array
[the Nine Yang Manual] 2019 Fudan University Applied Statistics real problem + analysis
实验五 类和对象
Reinforcement learning series (I): basic principles and concepts
ABA问题遇到过吗,详细说以下,如何避免ABA问题
Mixlab unbounded community white paper officially released
【黑马早报】上海市监局回应钟薛高烧不化;麦趣尔承认两批次纯牛奶不合格;微信内测一个手机可注册俩号;度小满回应存款变理财产品...
强化学习基础记录
Leetcode. 3. Longest substring without repeated characters - more than 100% solution
1. First knowledge of C language (1)
使用Spacedesk实现局域网内任意设备作为电脑拓展屏
FAQs and answers to the imitation Niuke technology blog project (I)
Meituan dynamic thread pool practice ideas, open source