Hello I don't understand what does the group by do?
I know it's not the time to ask this but please can anyone explain for me? For example what does the group by do in this code?
Thanks in advance for any feedback.
SELECT CASE WHEN elevation < 250 THEN 'Low' WHEN elevation BETWEEN 250 AND 1749 THEN 'Medium' WHEN elevation >= 1750 THEN 'High' ELSE 'Unknown' END AS elevation_tier , COUNT(*) FROM airports GROUP BY 1;