Create number-of-calls-between-two-persons.sql

Author: kamyu104

MySQL/number-of-calls-between-two-persons.sql

@@ -0,0 +1,10 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT LEAST(from_id,to_id) as person1,
+       GREATEST(from_id,to_id) as person2,
+       COUNT(*) as call_count,
+       SUM(duration) as total_duration
+FROM Calls
+GROUP BY person1, person2
+ORDER BY NULL;