August 2024
Intermediate to advanced
392 pages
10h 4m
Japanese
Content preview from 達人に学ぶDB設計徹底指南書 第2版
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保存」（118ページ）で説明したように、正規化は必ず可逆的な操作でなければな
りません。ボイス－コッド正規形への変換時は、気をつけないとこうした非可逆な
分解を行なってしまう危険があります。
37
この原因は、「チームコード」をキーにした結合が、「多対多」の関連になってし
まったからです。正規化は常に「1対多」の関連を生むようにテーブルを分割する
必要があります。この「1対多」「多対多」という関連の種類については、次章で
詳しく見ます。
000A 001 123W
000B 001 456Z
000B 002 003O
001F 001 123W
001F 002 003O
003O 002 999Y
それでは、正しい分解の仕方とはどのようなものでしょうか？
先ほどの失敗は、元のテーブル（上記）に存在していた以下の関数従属性を失っ
たために起きたことでした。
→
したがって、この関数従属性を保存することで、可逆的な分解が可能になります。
3
128
9
8
7
6
5
4
3
2
1
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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.