問89
頻出度★★☆
情報処理に関する用語 a～d のうち, 関係データベースの関係演算だけを全て挙げたものはどれか。 a 結合 b 射影 c 順次 d 選択
平成29年度 春期 ITパスポート試験 問89
テクノロジ系データベース › データ操作
This question's explanation and your answers so far.
解説
問 89
Incorrectア
a Join and b Projection are indeed relational operations, but these two alone omit d Selection, so they do not list all the relational operations. Selection is also a representative relational operation, so just a and b is insufficient.
Incorrectイ
a and b are relational operations, but the mistake is that it includes c Sequence. Sequence is one of the basic program control structures (sequence, selection, iteration), not a relational operation of a relational database.
- ウ
正解 The relational operations (relational algebra) of a relational database are operations performed on tables (relations); the representative ones are Selection, Projection, and Join. Selection (d) takes out the rows (records) that meet a condition, Projection (b) takes out the needed columns (items), and Join (a) links multiple tables by a common item, so all three are relational operations. On the other hand, c Sequence is not a relational operation. Therefore, the one that lists all and only the relational operations is a,b,d, and the correct answer is ウ.
Incorrectエ
a Join and d Selection are relational operations, but b Projection is missing. Projection is a representative relational operation that takes out the needed columns, so a,d without it does not list them all.
ここがポイント
- The basics of a relational database's relational operations (relational algebra) are three: Selection (narrow the rows), Projection (narrow the columns), and Join (link tables).
- This question tests the distinction that Sequence is not a relational operation but one of the basic program control structures (sequence, selection, iteration).
用語