Create customer-order-frequency.sql

Author: kamyu104

MySQL/customer-order-frequency.sql

@@ -0,0 +1,23 @@
+# Time:  O(n)
+# Space: O(n)
+
+SELECT a.customer_id,
+       a.name
+FROM Customers AS a
+INNER JOIN
+  (SELECT *
+   FROM Orders
+   WHERE order_date BETWEEN "2020-06-01" AND "2020-07-31" ) AS b
+ON a.customer_id = b.customer_id
+INNER JOIN Product AS c
+ON b.product_id = c.product_id
+GROUP BY a.customer_id
+HAVING SUM(CASE
+               WHEN LEFT(b.order_date, 7) = "2020-06" THEN c.price * b.quantity
+               ELSE 0
+           END) >= 100
+AND    SUM(CASE
+               WHEN LEFT(b.order_date, 7) = "2020-07" THEN c.price * b.quantity
+               ELSE 0
+           END) >= 100
+ORDER BY NULL;