Unit 4 · Database Management Systems Paper 2 CS · September 2022

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 computes the names of sailors who have reserved a red and a green boat?

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

Show answer & explanation

Correct answer: A. ρ(Tempred, π_sid((σ_color='red' Boats) ⋈ Reserves)); ρ(Tempgreen, π_sid((σ_{color='green'} Boats) ⋈ Reserves)); π_sname((Tempred ∩ Tempgreen) ⋈ Sailors)

Explanation

Intersect the sids that reserved a red boat with those that reserved a green boat. B, C and D intersect boats instead, and no boat is both red and green, so they return nothing.

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Which query computes the names of sailors who have reserved a red and a green boat?

Explanation

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