Ivanbyone · Ivanbyone · Jul 20, 2025 · Jul 20, 2025
diff --git a/README.md b/README.md
@@ -185,6 +185,7 @@ Useful for preparing for technical interviews and improving your SQL skills.
     - [3220. Odd and Even Transactions](./leetcode/medium/3220.%20Odd%20and%20Even%20Transactions.sql)
     - [3475. DNA Pattern Recognition](./leetcode/medium/3475.%20DNA%20Pattern%20Recognition.sql)
     - [3497. Analyze Subscription Conversion](./leetcode/medium/3497.%20Analyze%20Subscription%20Conversion.sql)
+    - [3601. Find Drivers with Improved Fuel Efficiency](./leetcode/medium/3601.%20Find%20Drivers%20with%20Improved%20Fuel%20Efficiency.sql)
 3. [Hard](./leetcode/hard/)
     - [185. Department Top Three Salaries](./leetcode/hard/185.%20Department%20Top%20Three%20Salaries.sql)
     - [601. Human Traffic of Stadium](./leetcode/hard/601.%20Human%20Traffic%20of%20Stadium.sql)

diff --git a/leetcode/medium/3601. Find Drivers with Improved Fuel Efficiency.sql b/leetcode/medium/3601. Find Drivers with Improved Fuel Efficiency.sql
@@ -0,0 +1,70 @@
+/*
+Question 3601. Find Drivers with Improved Fuel Efficiency
+Link: https://leetcode.com/problems/find-drivers-with-improved-fuel-efficiency/description/?envType=problem-list-v2&envId=database
+
+Table: drivers
+
++-------------+---------+
+| Column Name | Type    |
++-------------+---------+
+| driver_id   | int     |
+| driver_name | varchar |
++-------------+---------+
+driver_id is the unique identifier for this table.
+Each row contains information about a driver.
+Table: trips
+
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| trip_id       | int     |
+| driver_id     | int     |
+| trip_date     | date    |
+| distance_km   | decimal |
+| fuel_consumed | decimal |
++---------------+---------+
+trip_id is the unique identifier for this table.
+Each row represents a trip made by a driver, including the distance traveled and fuel consumed for that trip.
+Write a solution to find drivers whose fuel efficiency has improved by comparing their average fuel efficiency in the first half of the year with the second half of the year.
+
+Calculate fuel efficiency as distance_km / fuel_consumed for each trip
+First half: January to June, Second half: July to December
+Only include drivers who have trips in both halves of the year
+Calculate the efficiency improvement as (second_half_avg - first_half_avg)
+Round all results to 2 decimal places
+Return the result table ordered by efficiency improvement in descending order, then by driver name in ascending order.
+*/
+
+WITH first_avg AS (
+    SELECT 
+        driver_id,
+        AVG(distance_km::numeric / fuel_consumed) AS first_half_avg
+    FROM trips
+    WHERE trip_date < '2023-07-01'
+    GROUP BY driver_id
+),
+
+second_avg AS (
+    SELECT 
+        driver_id,
+        AVG(distance_km::numeric / fuel_consumed) AS second_half_avg
+    FROM trips
+    WHERE trip_date >= '2023-07-01'
+    GROUP BY driver_id
+)
+
+SELECT 
+    d.driver_id,
+    d.driver_name,
+    ROUND(fa.first_half_avg, 2) AS first_half_avg,
+    ROUND(sa.second_half_avg, 2) AS second_half_avg,
+    ROUND((sa.second_half_avg - fa.first_half_avg), 2) AS efficiency_improvement
+FROM first_avg AS fa
+INNER JOIN
+    second_avg AS sa
+    ON fa.driver_id = sa.driver_id
+LEFT JOIN
+    drivers AS d
+    ON fa.driver_id = d.driver_id
+WHERE (sa.second_half_avg - fa.first_half_avg) > 0
+ORDER BY efficiency_improvement DESC, d.driver_name ASC