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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解答のSQLは、大きく二つのパートに分かれています。一つ目が、HAVING
COUNT(*) >=よりも後のサブクエリ。このパートでは、取り扱い商品数が最も多
い支社の商品数を選択しています。その結果を受けて、HAVING 句より前のパー
トで、その最大商品数を持つ支店を選択しています。現在ではこの解答はウィンド
ウ関数を使っても書くことができます。余力のある人は考えてみてください（クエ
リの複雑度で言うと似たり寄ったりなのですが）。
解答の SQLの複雑な点は、以下の 2点です。
したがって、方針としてはこの二つを行なわないSQLを可能にするようなテー
ブル構成の変更です。これを実現するには、次のように「商品分類」テーブルに「商
品数」列を追加します。
C1 水洗用品 4
C2 食器 2
C3 書籍 1
C4 日用雑貨 1
このテーブルを前提にすれば、SQL 文は極限まで簡略化されます。
SELECT *
FROM
分
;
このテーブル変形は、本章の5-2 節で見たサマリデータをテーブルに保持する方
347
法と同一です。しかも、本文のサンプルで見たときには第 3 正規形を崩す形でサマ
リデータを保持していたのに対し、この例では正規 ...
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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.