Consider the following relational schemas: And the instances (snapshots) of…
Consider the following relational schemas:
And the instances (snapshots) of the above schemas:
Consider the following relational algebra query is executed on the above instance:
The number of rows return by above query is ________.
Answer: 3 — Step 1: Select red and green boatsFrom Boats table: Red boats → 102, 104 Green boats → 103 So, Tempboats = {102, 103, 104} Step 2: Join with Reserves Keep…
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Correct answer: 3
Step 1: Select red and green boats
From Boats table:
Red boats → 102, 104
Green boats → 103
So, Tempboats = {102, 103, 104}
Step 2: Join with Reserves
Keep only reservations where bid ∈ {102, 103, 104}
Matching rows:
22 → 102, 103, 104
31 → 102, 103, 104
64 → 102
74 → 103
Total matching rows = 8
Step 3: Join with Sailors (get names)
22 → Dustin
31 → Lubber
64 → Horatio
74 → Horatio
Names obtained (including duplicates):
Dustin (3 times)
Lubber (3 times)
Horatio (2 times)
Step 4: Apply projection π_sname
Projection removes duplicates.
Distinct names:
Dustin
Lubber
Horatio