Handling NULL Values in SQL | Dataford Interview Questions

How do you handle NULL values in SQL?

Asked in the Recruiter Screen stage. Write a SQL query using the provided tables to produce customer-level trip metrics for January 2025. Preserve customers with no qualifying trips, distinguish missing fares from zero fares, and exclude trips outside the reporting period or without a usable trip date.

Output

One row per customer, including customers with no qualifying trips.
Columns: customer_id, customer_name, total_trips, trips_with_fare, total_fare, average_fare, and latest_trip_date.
total_fare should be zero when no fare is available; average_fare should remain NULL when no non-NULL fare exists.
Order by customer_id ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name

trips

Column	Type	Description
trip_idPK	INT	Unique trip identifier
customer_id	INT	Customer associated with the trip
trip_date	DATE	Date on which the trip occurred
fare_amount	NUMERIC(10,2)	Recorded fare amount

Your question is Handling NULL Values in SQL. Start with the requirements and the two tables in the Question tab.

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Problem