Free Seats
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Let’s say you work for a small airline.
You’re given three tables: flights, planes, and flight_purchases.
Write a query to find the number of unpurchased seats for each flight.
For the purposes of this question, assume that there will be no entries in the flight_purchases table for flights or seats that do not exist.
Example:
Input:
flights table
| Column | Type |
|---|---|
id |
INTEGER |
plane_id |
INTEGER |
planes table
| Column | Type |
|---|---|
id |
INTEGER |
number_of_seats |
INTEGER |
flight_purchases table
| Column | Type |
|---|---|
flight_id |
INTEGER |
seat_id |
INTEGER |
Output:
| Column | Type |
|---|---|
flight_id |
INTEGER |
free_seats |
INTEGER |
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