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,
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.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.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.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.
3章入門：クエリ
ここまでの2つの章では、データベースクエリ（select文）の例をいくつか見てきました。本章では、select文のさまざまな要素とそれらの相互作用を少し詳しく見ていきます。本章を最後まで読めば、データの取得、結合、フィルタリング、グループ化、ソートの方法を基本的に理解できるはずです。4章から10章では、これらのトピックを詳しく見ていきます。
3.1 クエリの仕組み
select文の説明に入る前に、クエリがMySQLサーバーによって（またはその他のデータベースサーバーでも）どのように実行されるのかを見ておくとよいかもしれません。mysqlユーティリティを使っているとしたら（そうであると前提しますが）、すでにユーザー名とパスワードを入力してMySQLサーバーにログインしているはずです（MySQLサーバーを別のコンピュータ上で実行している場合は、ホスト名も必要です）。ユーザー名とパスワードが正しいことが確認されると、そのユーザーが使うためのデータベース接続（database connection）が作成されます。この接続は、接続をリクエストしたアプリケーションによって解放されるか、サーバーが接続を閉じるまで維持されます。つまり、接続が終了するのは、mysqlユーティリティでquitを入力するか、サーバーをシャットダウンしたときです。MySQLサーバーに対する接続にはそれぞれ識別子（ID）が割り当てられます。このIDは最初にログインしたときに表示されます。
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 11 Server version: 8.0.22 ...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,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
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.