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Databases and SQL: Question 6

Syllabus 9.2

Multiple choice 1 mark

Trailhead Bike Rentals stores every bike hire it makes in a single database table called BIKE_RENTAL, shown below.

RentalID CustomerName BikeType DurationHours HelmetRequested
R201 Priya Nair Mountain 2 True
R202 Owen Clarke Road 3 False
R203 Priya Nair Hybrid 1 True
R204 Maya Lindqvist Mountain 2 False

Which field should be chosen as the primary key for the BIKE_RENTAL table?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall what a primary key must do

A primary key must hold a value that is different for every record in the table, so that any single record can always be identified precisely.

Step 2: Check each candidate field for repeated values

  • CustomerName: “Priya Nair” appears twice (R201 and R203), so it repeats.
  • BikeType: “Mountain” appears twice (R201 and R204), so it repeats.
  • DurationHours: the value 2 appears twice (R201 and R204), so it repeats.
  • RentalID: R201, R202, R203 and R204 are all different from one another.

Step 3: Confirm the match

Only RentalID gives a genuinely different value for every record shown, and there is no reason to expect two rentals would ever share the same RentalID, so it is the only field able to serve reliably as the primary key.

Final answer

The primary key should be RentalID, option D.