Nice

The postgres documentation defines the return of count() as bigint.
I would stick with that official interpretation. https://www.postgresql.org/docs/8.2/functions-aggregate.html

Thanks :)

Very nice kata, tried it first months ago but could not understand what the level was supposed to be, came back to it today and managed to figure it out eventually.

Learned a lot, thanks :)

Right... Good call. In that case, the sales table should have a default for the department id field set to 0, and then the unknown row would have an ID of 0

Because id cannot be null in table departments (cause PK), then no values will be provided for result.

If the db is built properly, the departments table would have a null row that would have the name "Unknown"

done!

Python

Tell me the language you used to solve the kata.

Minor issue but while the description demands to say "You know nothing, Jon Snow"
this fails the test cases as there it checks for a different wording:
"Jon Snow, you know nothing"