Create the-most-frequently-ordered-products-for-each-customer.sql

Author: kamyu104

MySQL/the-most-frequently-ordered-products-for-each-customer.sql

@@ -0,0 +1,30 @@
+# Time:  O(n)
+# Space: O(n)
+
+WITH product_count_cte AS
+  (SELECT c.customer_id,
+          o.product_id,
+          p.product_name,
+          count(c.customer_id) AS product_cnt
+   FROM Customers c,
+        Orders o,
+        Products p
+   WHERE c.customer_id = o.customer_id
+     AND o.product_id = p.product_id
+   GROUP BY c.customer_id,
+            o.product_id
+   ORDER BY NULL)
+, max_product_count_cte AS
+  (SELECT customer_id,
+          max(product_cnt) AS product_cnt
+   FROM product_count_cte
+   GROUP BY customer_id
+   ORDER BY NULL)
+
+SELECT a.customer_id,
+       a.product_id,
+       a.product_name
+FROM product_count_cte a
+INNER JOIN max_product_count_cte b
+ON a.customer_id = b.customer_id AND
+   a.product_cnt = b.product_cnt;