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Relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries. This in contrast to the relational algebra which is also part of the relational model but provides a more procedural way for specifying queries. The relational algebra might suggest these steps to retrieve the phone numbers and names of book stores that supply ''Some Sample Book'': # Join book stores and titles over the BookstoreID. # Restrict the result of that join to tuples for the book ''Some Sample Book''. # Project the result of that restriction over StoreName and StorePhone. The relational calculus would formulate a descriptive, declarative way: :Get StoreName and StorePhone for supplies such that there exists a title BK with the same BookstoreID value and with a BookTitle value of ''Some Sample Book''. The relational algebra and the relational calculus are essentially logically equivalent: for any algebraic expression, there is an equivalent expression in the calculus, and vice versa. This result is known as Codd's theorem. == References == * 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Relational calculus」の詳細全文を読む スポンサード リンク
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