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Subqueries

Correlated Subqueries II

It would also be interesting to order flights by giving them a sequence number based on time, by carrier.

For instance, assuming flight_id increments with each additional flight, we could use the following query to view flights by carrier, flight id, and sequence number:

SELECT carrier, id,
    (SELECT COUNT(*)
FROM flights f
WHERE f.id < flights.id
AND f.carrier=flights.carrier) + 1
 AS flight_sequence_number
FROM flights;
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