April 2022
Beginner to intermediate
344 pages
9h 32m
Japanese
Content preview from はじめての設計をやり抜くための本 第2版 概念モデリングからアプリケーション、データベース、アーキテクチャ設計、アジャイル開発まで
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152
導
入
編
1
設
計
編
ア
キ
テ
ク
チ
ャ
編
2
3
4
5
6
7
3
第
2
正規形
第2正規形は、あるテーブルが第1正規形であり、なおかつすべての非
キーカラムがすべての候補キーに対して完全関数従属する場合のテーブルの
ことです。言い換えると、すべての非キーカラムがすべての候補キーに対し
て部分関数従属しないテーブルです。
また新しい用語が登場しましたね。「候補キー」と「完全関数従属」と
「部分関数従属」です。
候補キーとは、その行を一意に特定することができるカラム、もしくはカ
ラムの集合を指します。候補キーの中から1つが主キーになることができま
す。行には必ず候補キーが1つ以上あります。例えば、図3-27の社員テー
ブルには候補キーがいくつかあります。
社員番号
名前
所属
入社年月日
社会保険番号
社員
図
3
-
27
：社員テーブル
当然ですが、まずは主キーである社員番号です。また、社会保険番号も候
補キーです。社会保険番号は、社会保険庁が正しく管理している限り、一意
に特定できます。この2つは単独のカラムで候補キーになります。さらに、
所属している部署に同姓同名の人がいない場合は、所属IDと名前でも候補
キーになり得ます。
＜3つの候補キー＞
●社員番号
●社会保険番号
●所属IDと名前
153
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6
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.