Consider the following relation How many tuples will be result of following…
Consider the following relation
How many tuples will be result of following relation
Answer: 4 — Expression: (STUDENT ⨝ (AGE ≥ 25 ∧ STUDENT.SID = RESERVES.SID) RESERVES) ⨝ GATEEXAM Step-by-step reasoning: Apply the AGE ≥ 25 selection on STUDENT: keep…
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Correct answer: 4
Expression: (STUDENT ⨝ (AGE ≥ 25 ∧ STUDENT.SID = RESERVES.SID) RESERVES) ⨝ GATEEXAM
Step-by-step reasoning:
Apply the AGE ≥ 25 selection on STUDENT: keep students with SID = 12 (age 25), 15 (age 33), 16 (age 32), 25 (age 28).
Join these selected STUDENT rows with RESERVES on SID. Matching RESERVES rows are:
SID 12, GATEID 101, EXAM DATE 28/2/14
SID 15, GATEID 101, EXAM DATE 28/2/14
SID 25, GATEID 102, EXAM DATE 1/3/14
SID 16, GATEID 103, EXAM DATE 2/3/14
SID 12, GATEID 104, EXAM DATE 1/3/14
After this join there are 5 intermediate tuples (one student can appear multiple times if they have multiple reservations).
Now join with GATEEXAM on GATEID. GATEEXAM contains GATEID values 101, 102, 103. The RESERVES row with GATEID 104 has no match and is eliminated.
Remaining joined tuples (final result):
SID 12, GATEID 101, EXAM DATE 28/2/14
SID 15, GATEID 101, EXAM DATE 28/2/14
SID 25, GATEID 102, EXAM DATE 1/3/14
SID 16, GATEID 103, EXAM DATE 2/3/14
Total tuples in the final result: 4.