Q20

MSQ1 mark

Let $P, Q, R$ and $S$ be the attributes of a relation in a relational schema. Let $X \rightarrow Y$ indicate functional dependency in the context of a relational database, where $X, Y \subseteq\{P, Q, R, S\}$ . Which of the following options is/are always true?

(A)

If $(\{P, Q\} \rightarrow\{R\}$ and $\{P\} \rightarrow\{R\})$ , then $\{Q\} \rightarrow\{R\}$

(B)

If $\{P, Q\} \rightarrow\{R\}$ , then $(\{P\} \rightarrow\{R\}$ or $\{Q\} \rightarrow\{R\})$

(C)

If $(\{P\} \rightarrow\{R\}$ and $\{Q\} \rightarrow\{S\})$ , then $\{P, Q\} \rightarrow\{R, S\}$

(D)

If $\{P\} \rightarrow\{R\}$ , then $\{P, Q\} \rightarrow\{R\}$

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