4. count(case when)


#1

https://www.codecademy.com/courses/sql-table-transformation/lessons/conditional-aggregates/exercises/count-case-when?action=lesson_resume

I’m not sure what the “1” represents after the “WHEN elevation < 1000 THEN”. I’ve tried replacing the “1” with multiple different numbers and the output is still the same.



select state,
	count(case when elevation < 1000 then 1 else null
  end) as count_low_elevation_airports
  from airports
  group by state;



#2

That is because the null cases are not included in the count. 1 or any other non-zero number equates to a boolean true, or NOT NULL.


#3

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