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Home Database Mysql Tutorial 秒懂?dāng)?shù)據(jù)庫三范式

秒懂?dāng)?shù)據(jù)庫三范式

Jun 07, 2016 pm 03:59 PM
mysql database paradigm

本篇文章給大家?guī)淼膬?nèi)容是介紹數(shù)據(jù)庫設(shè)計(jì)的三大范式,讓大家了解理解三大范式數(shù)據(jù)庫的三大范式。有一定的參考價(jià)值,有需要的朋友可以參考一下,希望對(duì)你們有所幫助。

數(shù)據(jù)庫設(shè)計(jì)范式

什么是范式:

簡言之就是,數(shù)據(jù)庫設(shè)計(jì)對(duì)數(shù)據(jù)的存儲(chǔ)性能,還有開發(fā)人員對(duì)數(shù)據(jù)的操作都有莫大的關(guān)系。所以建立科學(xué)的,規(guī)范的的數(shù)據(jù)庫是需要滿足一些規(guī)范的來優(yōu)化數(shù)據(jù)數(shù)據(jù)存儲(chǔ)方式。在關(guān)系型數(shù)據(jù)庫中這些規(guī)范就可以稱為范式?!鞠嚓P(guān)視頻教程推薦:mysql教程】

三大范式是什么:

第一范式:當(dāng)關(guān)系模式R的所有屬性都不能在分解為更基本的數(shù)據(jù)單位時(shí),稱R是滿足第一范式的,簡記為1NF。滿足第一范式是關(guān)系模式規(guī)范化的最低要求,否則,將有很多基本操作在這樣的關(guān)系模式中實(shí)現(xiàn)不了。

第二范式:如果關(guān)系模式R滿足第一范式,并且R得所有非主屬性都完全依賴于R的每一個(gè)候選關(guān)鍵屬性,稱R滿足第二范式,簡記為2NF。

第三范式:設(shè)R是一個(gè)滿足第一范式條件的關(guān)系模式,X是R的任意屬性集,如果X非傳遞依賴于R的任意一個(gè)候選關(guān)鍵字,稱R滿足第三范式,簡記為3NF.

注:關(guān)系實(shí)質(zhì)上是一張二維表,其中每一行是一個(gè)元組,每一列是一個(gè)屬性

理解三大范式

第一范式

? ?1、每一列屬性都是不可再分的屬性值,確保每一列的原子性

? ?2、兩列的屬性相近或相似或一樣,盡量合并屬性一樣的列,確保不產(chǎn)生冗余數(shù)據(jù)。

如果需求知道那個(gè)省那個(gè)市并按其分類,那么顯然第一個(gè)表格是不容易滿足需求的,也不符合第一范式。

顯然第一個(gè)表結(jié)構(gòu)不但不能滿足足夠多物品的要求,還會(huì)在物品少時(shí)產(chǎn)生冗余。也是不符合第一范式的。

第二范式

每一行的數(shù)據(jù)只能與其中一列相關(guān),即一行數(shù)據(jù)只做一件事。只要數(shù)據(jù)列中出現(xiàn)數(shù)據(jù)重復(fù),就要把表拆分開來。

一個(gè)人同時(shí)訂幾個(gè)房間,就會(huì)出來一個(gè)訂單號(hào)多條數(shù)據(jù),這樣子聯(lián)系人都是重復(fù)的,就會(huì)造成數(shù)據(jù)冗余。我們應(yīng)該把他拆開來。

這樣便實(shí)現(xiàn)啦一條數(shù)據(jù)做一件事,不摻雜復(fù)雜的關(guān)系邏輯。同時(shí)對(duì)表數(shù)據(jù)的更新維護(hù)也更易操作。

第三范式

?數(shù)據(jù)不能存在傳遞關(guān)系,即沒個(gè)屬性都跟主鍵有直接關(guān)系而不是間接關(guān)系。像:a-->b-->c ?屬性之間含有這樣的關(guān)系,是不符合第三范式的。

比如Student表(學(xué)號(hào),姓名,年齡,性別,所在院校,院校地址,院校電話)

這樣一個(gè)表結(jié)構(gòu),就存在上述關(guān)系。 學(xué)號(hào)-->?所在院校 --> (院校地址,院校電話)

這樣的表結(jié)構(gòu),我們應(yīng)該拆開來,如下。

(學(xué)號(hào),姓名,年齡,性別,所在院校)--(所在院校,院校地址,院校電話)

最后:

三大范式只是一般設(shè)計(jì)數(shù)據(jù)庫的基本理念,可以建立冗余較小、結(jié)構(gòu)合理的數(shù)據(jù)庫。如果有特殊情況,當(dāng)然要特殊對(duì)待,數(shù)據(jù)庫設(shè)計(jì)最重要的是看需求跟性能,需求>性能>表結(jié)構(gòu)。所以不能一味的去追求范式建立數(shù)據(jù)庫。

總結(jié):以上就是本篇文章所介紹的秒懂?dāng)?shù)據(jù)庫三范式的全部內(nèi)容,希望能對(duì)大家的學(xué)習(xí)有所幫助。更多請(qǐng)關(guān)注php中文網(wǎng)其它相關(guān)文章!

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