Consider the following two relations, R(A,B) and S(A,C): R A B 10 20 20 30 30…
2024
Consider the following two relations, R(A,B) and S(A,C):
R
A B
10 20
20 30
30 40
30 50
30 95
S
A C
10 90
30 45
40 80
The total number of tuples obtained by evaluating the following expression
is _________
Attempted by 73 students.
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Correct answer: 2
Key idea: join R and S on A, then count joined tuples where B < C.
A = 10: R has (10,20) and S has (10,90) → joined tuple (10,20,90). 20 < 90, so this contributes 1 tuple.
A = 30: R has (30,40), (30,50), (30,95) and S has (30,45). Joined tuples are (30,40,45), (30,50,45), (30,95,45). Only 40 < 45 holds, so this contributes 1 tuple.
Other A values produce no matching pairs, so they contribute 0 tuples.
Total number of tuples satisfying B < C after the join: 2
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