R1(Name, Class) = {(a1, 9), (b1, 5), (c1, 6), (d1, 11)} and R2(Name, Class) = {(b1, 5), (f1, 8)}. Which operation produces the output {(b1, 5)}?

1. AR1 R2
2. BR1-R2
3. CR 1-(R 1-R 2)
4. DR1 U R2

Pick an option to check yourself, or open the answer below.

Show answer & explanation

Correct answer: A. R1 R2

Explanation

Only (b1, 5) is in both relations, so the output is R1 ∩ R2.

Note: Option C, R1 − (R1 − R2), also equals R1 ∩ R2 and produces the same output.