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1. |
Let R and S be two relations with the following schemaR (P, Q, R1, R2, R3)S (P, Q, S1, S2)Where {P, Q} is the key for both schemas. Which of the following queries are equivalent?I) ΠP (R ⋈ S)II) ΠP (R) ⋈ ΠP (S)III) ΠP (ΠP, Q (R) ∩ ΠP, Q (S))IV) ΠP (ΠP, Q (R) - (ΠP, Q (R) - ΠP, Q (S))) |
A. | Only I) and II) |
B. | Only I) and III) |
C. | Only I), II) and III) |
D. | Only I), III) and IV) |
Answer» E. | |