January 2021
Intermediate
240 pages
5h 32m
Japanese
Content preview from 図解まるわかり データベースのしくみ
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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.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.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.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.
152
2
別の種類の項目を分割する
5-12
テーブルの中には、値がわかると特定の行に絞り込めるカラムがありま
す。その
。その結果を2 といいます。
図5-21 のように商品の在庫を管理するテーブルの項目に店舗名、商品
名、商品価格、在庫数がある場合、この項目のうち店舗名と商品名さえわ
かれば、1つのレコードに絞り込むことができます。そして、これらの項
目に対応している項目を分離させますが、今回は商品名に対して価格が対
応していますので、第2 正規形のステップで別テーブルに分離させます。
従属関係を取り除くことで、別の種類のデータを分けて管理することが
できます。例えば新商品が入荷したときに、商品名と価格をあらかじめ登
録することが可能です。もし注文テーブルにまとめて商品情報を登録して
いたら、新商品が入荷しても注文がないと商品情報の登録ができません
し、
。第2 正規形にすることによってこれら
の問題点がなくなり、データを管理しやすい形に直すことができます。
図5-22 で考えると、レコードを1 つに特定できるカラムは講義名と学
生IDです。このうち講義名は教員名と教員連絡先に、学生IDは学生名と
対応しています。これらの従属関係になっている項目を抜き出して別のテ
ーブルに分離します。すると講義ごとの受講学生一覧テーブルと講義テー ...
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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.