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Aggregate Across Multiple Tables
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Aggregate Across Multiple Tables

MediumSQL · PostgreSQL

Problem

Write a SQL query to aggregate data from multiple tables.

Use the provided city, station, and trip tables. Include every city, even when it has no matching station or qualifying trip. Consider only completed trips that started during January 2026.

Output

  1. One row per city.
  2. Columns: city_name, completed_trip_count, total_fare, and average_fare.
  3. Use zero for cities without qualifying fares, and NULL for an undefined average.
  4. Order by total_fare descending, then city_name ascending.

Schema

cities
ColumnTypeDescription
city_idPKINTUnique city identifier
city_nameVARCHAR(100)City name
stations
ColumnTypeDescription
station_idPKINTUnique station identifier
station_nameVARCHAR(100)Station name
city_idINTOwning city identifier
trips
ColumnTypeDescription
trip_idPKINTUnique trip identifier
station_idINTStarting station identifier
trip_statusVARCHAR(20)Trip status
trip_started_atTIMESTAMPTrip start timestamp
fare_amountNUMERIC(10,2)Fare charged for the trip
Tablescitiesstationstrips
Interviewer

Your question is Aggregate Across Multiple Tables. Start with the requirements and the three tables in the Question tab.

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