Directions (Q31–35): Consider the relational schema of Sailors S, Reserves R and Boats B.
Table 1: Sailors
| Sid | Sname | Rating | Age |
|---|---|---|---|
| 22 | Dustin | 7 | 45.0 |
| 29 | Brutus | 1 | 33.0 |
| 31 | Lubber | 8 | 55.5 |
| 32 | Andy | 8 | 25.5 |
| 58 | Rusty | 10 | 35.5 |
| 64 | Horatio | 7 | 35.5 |
| 71 | Zorba | 10 | 16.0 |
| 74 | Horatio | 9 | 35.0 |
| 85 | Art | 3 | 25.5 |
| 95 | Bob | 3 | 63.5 |
Table 2: Reserves
| Sid | Bid | Day |
|---|---|---|
| 22 | 101 | 10/10/98 |
| 22 | 102 | 10/10/98 |
| 22 | 103 | 10/8/98 |
| 22 | 104 | 10/7/98 |
| 31 | 102 | 11/10/98 |
| 31 | 103 | 11/6/98 |
| 31 | 104 | 11/12/98 |
| 64 | 101 | 9/5/98 |
| 64 | 102 | 9/8/98 |
| 74 | 103 | 9/8/98 |
Table 3: Boats
| Bid | Bname | Color |
|---|---|---|
| 101 | Interlake | blue |
| 102 | Interlake | red |
| 103 | Clipper | green |
| 104 | Marine | red |
Which query/queries compute the names of sailors who have reserved boat 103?
Q1: πsname((σbid=103 Boats) ⋈ Sailors)
Q2: πsname(σbid=103(Reserves ⋈ Sailors))
Q3: πsname((σbid=103 Reserves) ⋈ Sailors)
Pick an option to check yourself, or open the answer below.
Show answer & explanation
Correct answer: B. Both Q2 and Q3
Explanation
Q2 and Q3 select bid = 103 from reservations (before or after the join). Q1 never uses Reserves; Boats ⋈ Sailors has no common attribute, so it is a cross product listing every sailor.More Database Management Systems questions
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