GATE DS&AI 2024 | Question: 16

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 $\phi$ denotes the empty set?

• A. $\Pi_{\text {name }}($ Team $) \backslash\left(\Pi_{\text {name }}(\right.$ Defender $) \cap \Pi_{\text {name }}($ Forward $\left.)\right)=\phi$
• B. $\left(\Pi_{\text {name }}(\right.$ Defender $) \cap \Pi_{\text {name }}($ Forward $\left.)\right) \backslash \Pi_{\text {name }}($ Team $)=\phi$
• C. $\Pi_{\text {name }}($ Team $) \backslash\left(\Pi_{\text {name }}(\right.$ Defender $) \cup \Pi_{\text {name }}($ Forward $\left.)\right)=\phi$
• D. $\left(\Pi_{\text {name }}(\right.$ Defender $) \cup \Pi_{\text {name }}($ Forward $\left.)\right) \backslash \Pi_{\text {name }}($ Team $)=\phi$

Answer 1

D

Comments

Every name occuring in team occurs in either defender or forward. So option C looks correct here not option D since it is saying names comes in team are a subset of names in defender or forward. Kindly check and confirm.