Create the-most-recent-three-orders.sql

Author: kamyu104

MySQL/the-most-recent-three-orders.sql

@@ -0,0 +1,25 @@
+# Time:  O(nlogn)
+# Space: O(n)
+
+SELECT customer_name,
+       customer_id,
+       order_id,
+       order_date
+FROM
+  (SELECT @accu := (CASE
+                        WHEN co.customer_id = @prev THEN @accu + 1
+                        ELSE 1
+                    END) AS n,
+          @prev := co.customer_id AS customer_id,
+          co.name AS customer_name,
+          co.order_id AS order_id,
+          co.order_date AS order_date
+   FROM
+     (SELECT @accu := 0, @prev := 0) AS init,
+     (SELECT c.name, c.customer_id, o.order_id, o.order_date FROM
+      Customers c
+      INNER JOIN Orders o
+      ON c.customer_id = o.customer_id
+      ORDER BY c.name ASC, c.customer_id ASC, o.order_date DESC) AS co
+  ) AS tmp
+WHERE n < 4;