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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このような問題を解決する手段として利用されるのが、（surrogate
key）です。「サロゲートキー」とも呼びます。これは名前のとおり、入力データに
最初から存在しているキー
の「代理」として新たに追加するキーです。ため
しに、先ほどの「市町村」テーブルに、代理キーとして「市町村管理コード」とい
う整数型の代理キーを追加してみましょう。
すると、たとえば
のケースは、以下のように市町村管理コードを主
キーとして使うことで、市町村コードに重複が発生しても問題がなくなります。
0 A000 A市 100,000
1 A001 B市 120,000
2 A002 C町 30,000
3 A003 D村 10,000
999 A999 Z市 15,000
⋮
0 A000 A市 100,000
1 A001 B市 120,000
2 A002 C町 30,000
3 A003 D村 10,000
999 A999 Z市 15,000
1000 A001 Q市 180,000
⋮
市町村コード「A001」が再利用されて重複が発生する場合にも、一意な連番を
割り振ることに決めた市町村管理コードが一意に保たれています。同様のことが、
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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.