search
HomeDatabaseMysql Tutorial第一范式、第二范式、第三范式

第一范式、第二范式、第三范式 第一范式 如果一个关系模式R的所有属性都是不可分的基本数据项,则R1NF(即R符合第一范式)。 两点: 一、每个字段都只能存放单一值 课程有两个值,不符合第一范式,可改为如下 二、每笔记录都要能利用一个惟一的主键来加以识别

第一范式、第二范式、第三范式

第一范式

如果一个关系模式R的所有属性都是不可分的基本数据项,则R∈1NF(即R符合第一范式)。

两点:

一、每个字段都只能存放单一值

\

课程有两个值,不符合第一范式,可改为如下

\

二、每笔记录都要能利用一个惟一的主键来加以识别

\

这里出现了重复组,同样不满足第一范式,因为缺乏唯一标识码,可改为

\

第二范式 

若关系模式R∈1NF(即R符合第一范式),并且每一个非主属性都完全依赖于R的码,则R∈2NF(即R符合第二范式)。

\

这里表的码为(学号,课程), 即知道这两项可以确定系名、宿舍、分数,或者是这三项依赖于前两项,可知

分数完全依赖(学号,课程)系名部分依赖(学号,课程),即知道学号或者课程就能确定系名.宿舍楼部分依赖(学号,课程),即知道学号或者课程就能确定宿舍楼.

由于非主属性系名,宿舍楼不完全依赖与码,不符合第二范式,可改为

表1

\

第三范式

若关系模式R∈3NF(即R符合第三范式),则每一个非主属性既不部分依赖于码也不传递依赖于码。

\

上面的表2不符合第三范式,这是因为你知道了系名,同样也就知道了宿舍楼,称宿舍楼传递依赖于码(学号),可分解为

\

 
Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
How to solve the problem of mysql cannot open shared libraryHow to solve the problem of mysql cannot open shared libraryMar 04, 2025 pm 04:01 PM

This article addresses MySQL's "unable to open shared library" error. The issue stems from MySQL's inability to locate necessary shared libraries (.so/.dll files). Solutions involve verifying library installation via the system's package m

Reduce the use of MySQL memory in DockerReduce the use of MySQL memory in DockerMar 04, 2025 pm 03:52 PM

This article explores optimizing MySQL memory usage in Docker. It discusses monitoring techniques (Docker stats, Performance Schema, external tools) and configuration strategies. These include Docker memory limits, swapping, and cgroups, alongside

How do you alter a table in MySQL using the ALTER TABLE statement?How do you alter a table in MySQL using the ALTER TABLE statement?Mar 19, 2025 pm 03:51 PM

The article discusses using MySQL's ALTER TABLE statement to modify tables, including adding/dropping columns, renaming tables/columns, and changing column data types.

Run MySQl in Linux (with/without podman container with phpmyadmin)Run MySQl in Linux (with/without podman container with phpmyadmin)Mar 04, 2025 pm 03:54 PM

This article compares installing MySQL on Linux directly versus using Podman containers, with/without phpMyAdmin. It details installation steps for each method, emphasizing Podman's advantages in isolation, portability, and reproducibility, but also

What is SQLite? Comprehensive overviewWhat is SQLite? Comprehensive overviewMar 04, 2025 pm 03:55 PM

This article provides a comprehensive overview of SQLite, a self-contained, serverless relational database. It details SQLite's advantages (simplicity, portability, ease of use) and disadvantages (concurrency limitations, scalability challenges). C

How do I configure SSL/TLS encryption for MySQL connections?How do I configure SSL/TLS encryption for MySQL connections?Mar 18, 2025 pm 12:01 PM

Article discusses configuring SSL/TLS encryption for MySQL, including certificate generation and verification. Main issue is using self-signed certificates' security implications.[Character count: 159]

Running multiple MySQL versions on MacOS: A step-by-step guideRunning multiple MySQL versions on MacOS: A step-by-step guideMar 04, 2025 pm 03:49 PM

This guide demonstrates installing and managing multiple MySQL versions on macOS using Homebrew. It emphasizes using Homebrew to isolate installations, preventing conflicts. The article details installation, starting/stopping services, and best pra

What are some popular MySQL GUI tools (e.g., MySQL Workbench, phpMyAdmin)?What are some popular MySQL GUI tools (e.g., MySQL Workbench, phpMyAdmin)?Mar 21, 2025 pm 06:28 PM

Article discusses popular MySQL GUI tools like MySQL Workbench and phpMyAdmin, comparing their features and suitability for beginners and advanced users.[159 characters]

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

Repo: How To Revive Teammates
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

Atom editor mac version download

Atom editor mac version download

The most popular open source editor

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor