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GATE DA 2024 Q26: Relational algebra check that every team name is a player

Question

Consider a database that includes the following relations:

Defender(name, rating, side, goals)

Forward(name, rating, assists, goals)

Team(name, club, price)

Which ONE of the following relational algebra expressions checks that every name occurring in Team appears in either Defender or Forward, where ϕ\phi denotes the empty set?

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Answer: C (official GATE 2024 final answer key)

Concept used: Set containment in relational algebra: A⊆BA \subseteq B exactly when A∖B=ϕA \setminus B = \phi.

First step: "Appears in either Defender or Forward" is the union of the two name sets; Team's names must be contained in it.

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Source: official GATE 2024 DA question paper and final answer key, organised by IISc Bangalore. Question paper · Answer key

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