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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8-4
次のグレーノウハウは、アドホックな集計キーです。これは、BI/DWH 分野の
論理設計を行なう際によく問題になります。例として、こんなケースを考えましょ
う。
今、都道府県別の人口を保持するテーブルがあるとします。このテーブルから、
県別ではなく地方別の人口の合計を求めるとします。つまり、東北＝北海道＋青森
＋岩手、東海＝静岡＋愛知＋三重、といったようにです。
01 北海道 550
02 青森 130
03 岩手 133
22 静岡 370
23 愛知 740
24 三重 185
36 徳島 78
37 香川 99
こうした集計をSQLで行なうには、集約関数とGROUP BY句を組み合わせれば
良いのですが、肝心の集計キーにすべき「地方コード」が存在していません。こう
いう場合、一番安直な解としては、次のように「地方コード」列を追加する、とい
うことになります。便宜的に地方コード01：東北、02：東海、03：四国とすると、
次のようになります。
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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.