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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では次に、このテーブルにもう一つ、「製品コード」という列を追加してみましょ
う。これは、社員が開発に当たっている製品を表わすもので、一人の社員が複数の
製品開発に携わることもあれば、一つの製品を複数の社員が共同開発していること
もあります。
000A 001 P1
000A 001 P2
000B 001 P1
000B 002 P1
001F 001 P2
001F 002 P2
003O 002 P2
003O 002 P3
この「社員 - チーム- 製品」テーブルにおいても、やはり第3 正規形（およびボイ
ス－コッド正規形）が成立していることを確認しておきましょう。{ 社員 ID, チーム
コード, 製品コード }の3列で主キーが構成されるため、やはり主キーだけのテー
ブルということになります（このように主キーだけで構成されうるのは、関連エン
ティティの特徴です。もちろん、主キー以外の属性を関連エンティティが持つこと
もありえますが）。
しかし、「社員-チーム-製品」テーブルには、これまで見てきた下位の正規形
において発生してきたのと同様、更新時の問題が発生します。たとえば、社員
「000A」がチームを「001」から「002」へ異動することになった場合、複数行に
対する更新が発生します。これはデータの保持が冗長であることを意味しており、 ...
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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.