FAQ: Subqueries - Correlated Subqueries II


This community-built FAQ covers the “Correlated Subqueries II” exercise from the lesson “Subqueries”.

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This exercise can be found in the following Codecademy content:

SQL: Table Transformation

FAQs on the exercise Correlated Subqueries II

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I just don’t understand what this question was ? " Using the same pattern, write a query to view flights by origin, flight id, and sequence number. Alias the sequence number column as `flight_sequence_number .". I had to get the solution to see what the code was doing. I seriously did not follow this chapter so far. There should be better examples.

Thank you
Sivarama Krishnan (kvsrkrishnan)


I had the same problem, and have been having similar problems with the next few lessons as well.


SELECT origin, id,
FROM flights f
WHERE f.id < flights.id
AND f.origin=flights.origin) + 1
AS flight_sequence_number
FROM flights;

Here we query based on origin and id rather than carrier and id as shown in the example.


But what does that achieve? What are you trying to query here? The Correlated subqueries are used for row-by-row processing, so for every orgin and id in the outer query… what are you executing in the inner query?


Can somebody explain the inner query and atleast 2 iterations please ?


I do agree with you. no explanation why the code is as it is… (unless i’ve skipped a bit)
why the ‘AS f’
why the ‘a.’

i can copy and paste and replace well, but it doesn’t mean i understand what is happening…
Guess i’ll have to read around other forums to find out why…
Its a bit disappointing, not as well thought through (or perhaps properly tested) as the initial SQL course…