July 2021
Intermediate to advanced
376 pages
6h 34m
Japanese
Content preview from 初めてのSQL 第3版Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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7章データの生成、操作、変換
「はじめに」で述べたように、本書の目的は、複数のデータベースサーバーで利用できる一般的なSQLテクニックを教えることにあります。本章では、文字列データ、数値データ、時間データの生成、変換、操作について説明しますが、この機能をカバーしているコマンドはSQL言語には含まれていません。データの生成、変換、操作には、代わりに組み込み関数を使います。SQL規格に含まれている関数もありますが、データベースベンダーが関数仕様に準拠していないというのはよくあることです。
そこで本章では、SQL文を使ってデータを生成して操作するための一般的な方法を確認した後、SQL Server、Oracle Database、MySQLが実装している組み込み関数の一部を具体的に見ていきます。本章を読むのに併せて、手持ちのデータベースサーバーに実装されている関数のリファレンスガイドをぜひダウンロードしてください。使っているデータベースサーバーが1つではない場合は、Kevin Kline他著『SQL in a Nutshell』やJonathan Gennick著『SQL Pocket Guide』（どちらもO'Reilly Media, Inc.）など、複数のデータベースサーバーをカバーしているリファレンスガイドが参考になるでしょう。
7.1 文字列データを操作する
文字列データを操作するときには、次の文字データ型のいずれかを使います。
- char
- 末尾をスペースで埋めた固定長の文字列を保持する。MySQLでは最大255文字、Oracle Databaseでは最大2,000文字、SQL Serverでは最大8,000文字の長さの文字列を保持できる。
- varchar
- 可変長の文字列を保持する。MySQLでは最大65,535文字、Oracle ...
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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.