Create find-peak-calling-hours-for-each-city.sql

Author: kamyu104

MySQL/find-peak-calling-hours-for-each-city.sql

@@ -0,0 +1,23 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+WITH call_by_hour_cte AS (
+    SELECT city, 
+           HOUR(call_time) AS calling_hour,
+           COUNT(*) AS number_of_calls
+    FROM Calls
+    GROUP BY 1, 2
+    ORDER BY NULL
+),
+rank_calling_hour_cte AS (
+    SELECT *,
+           DENSE_RANK() OVER (PARTITION BY city ORDER BY number_of_calls DESC) AS rnk
+    FROM call_by_hour_cte
+)
+
+SELECT city, 
+       calling_hour AS peak_calling_hour,
+       number_of_calls
+FROM rank_calling_hour_cte
+WHERE rnk = 1
+ORDER BY 2 DESC, 1 DESC;