solution to both problems

01-TopTravellers.sql

@@ -0,0 +1,6 @@
+-- Problem 1: Top Travellers (https://leetcode.com/problems/top-travellers/)
+select name, ifnull(sum(r.distance), 0) as travelled_distance 
+from users u
+left join rides r on u.id = r.user_id
+group by u.id
+order by travelled_distance desc, name asc

02-ApplesAndOranges.sql

@@ -0,0 +1,27 @@
+-- cte
+with apples as(
+    select sale_date, fruit as apple, sold_num as a_num 
+    from sales where fruit = 'apples'
+),
+oranges as (
+    select sale_date, fruit as oranges, sold_num as o_num 
+    from sales where fruit = 'oranges'
+)
+select apples.sale_date, (a_num - o_num) as diff
+from apples
+join oranges on apples.sale_date=oranges.sale_date
+order by sale_date 
+
+-- solution 2
+select a.sale_date, a.sold_num - b.sold_num as diff
+from sales a  
+join sales b on a.sale_date = b.sale_date
+where a.fruit = 'apples' and b.fruit = 'oranges'
+
+-- better version
+select sale_date, 
+sum (case when fruit='apples' then sold_num else 0 end) -
+sum (case when fruit='oranges' then sold_num else 0 end) as diff
+from sales
+group by sale_date
+order by sale_date