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データベース ざっくり解説 2リレーショナル代数

Last updated at Posted at 2019-12-09

和・差

image.png

直積

属性が被ってもよい。
イメージ的にはRとSの組み合わせ

image.png

射影・選択

射影は、列を取り出す
選択は、行を取り出す

自然結合

「選択」でしぼりこんで「射影」で片方だけ取る

image.png

共通部分

和両立条件を満たさなければならない
すべて同じ属性を持っている行を取り出す

image.png

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