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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120
切り離せない処理をまとめる
4-14
データベースに対して行われる複数の処理をまとめたものをトランザク
ションと呼びます。SQL は1 文ずつ実行することができますが、
1
ことができます（図4-27）。
銀行口座の例で考えてみましょう。A口座からB口座に10 万円を送金す
ると、データベース上では「A口座の預金をマイナス10 万円にする」「 B口
座の預金をプラス10 万円にする」といった 2 つの処理を同時に実行させる
必要があります。ところが、もしA口座の処理が完了した直後にシステム
に問題が発生し、B口座の処理が実行されないとB口座に送金額が反映さ
れなくなってしまうということが起こります（図4-28）。これらの処理を
トランザクションによってまとめて完了させることで、データが合わなく
なる問題を防ぐことができます。
トランザクションには以下のような特性があります。
原子性
トランザクションに含まれる処理が「すべて実行される」か「すべ
て実行されない」かのどちらかになる。
一貫性
あらかじめ設定された条件を満たし、データの整合性を保証する。
独立性
処理の途中経過が隠蔽され、外部からは結果だけ見ることができ
る。処理の実行途中の状態で、他の処理に影響を与えない。
永続性
トランザクションが完了したら、その結果が失われることはない。
複数の処理をまとめるトランザクシ
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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.