Consider a database that includes the following relations: Defender(name,…

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 denotes the empty set?

  1. A.

    Π𝑛𝑎𝑚𝑒 (Team) \ (Π𝑛𝑎𝑚𝑒 (Defender)∩ Π𝑛𝑎𝑚𝑒 (Forward)) = 𝜙

  2. B.

    (Π𝑛𝑎𝑚𝑒 (Defender)∩ Π𝑛𝑎𝑚𝑒 (Forward)) \ Π𝑛𝑎𝑚𝑒 (Team) = 𝜙

  3. C.

    Π𝑛𝑎𝑚𝑒 (Team) \ (Π𝑛𝑎𝑚𝑒 (Defender)∪ Π𝑛𝑎𝑚𝑒 (Forward)) = 𝜙

  4. D.

    (Π𝑛𝑎𝑚𝑒 (Defender)∪ Π𝑛𝑎𝑚𝑒 (Forward)) \ Π𝑛𝑎𝑚𝑒 (Team) = 𝜙

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