Create number-of-times-a-driver-was-a-passenger.sql

Author: kamyu104

MySQL/number-of-times-a-driver-was-a-passenger.sql

@@ -0,0 +1,9 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT d.driver_id,
+       COUNT(r2.passenger_id) AS cnt
+FROM   (SELECT DISTINCT r1.driver_id FROM Rides r1) d
+       LEFT JOIN Rides r2 ON d.driver_id = r2.passenger_id
+GROUP BY d.driver_id
+ORDER BY NULL;