January 2021
Intermediate
240 pages
5h 32m
Japanese
Content preview from 図解まるわかり データベースのしくみ
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68
データを更新する
3-11
テーブルに保存されているレコードはことが
できます。例えばユーザーの連絡先が変わったときに、ユーザー情報を保
存しているテーブルの情報を変更したいときや、間違えて登録してしまっ
たデータを後から修正したいときは、テーブルに保存されているデータを
更新します。
テーブルに保存されているレコードを更新するときは、「UPDATE」
文を使います。更新対象のテーブル名やカラム名、更新後の値、更新した
いレコードの条件を指定して使います。
図3-26は「menus」テーブルで「id」カラムの値が「1」に一致するデー
タを更新する例で、「name」カラムの値を「シチュー」に変更しています。
このように「SET」の後ろに更新対象のカラムと変更後の値を指定します。
更新後の値を指定するときは、「id= 2, name=' シチュー'」のようにカン
マ（,）で区切って複数のカラム名と値を指定することもできます。
「UPDATE」文は、3-8 で解説した「WHERE」を組み合わせて更新対象
のレコードを指定することが多いです。上の例では「id」カラムが「1」
のレコードを更新対象として指定しましたが、他にも演算子を使って、さ
まざまな検索条件を更新対象として指定することができます。
図3-27 は「users」テーブルで「age」カラムの値が「30」以上のレコ
ードの「status」カラムの値を「1」に更新する例です。他にも「WHERE ...
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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.