product-price-at-a-given-date.sql

Author: the1Riddle

MySQL/product-price-at-a-given-date.sql

@@ -1,17 +1,32 @@
+/*
 # Time:  O(mlogn), m is the number of unique product id, n is the number of changed dates
 # Space: O(m)
+       */
+
+SELECT 
+    t1.product_id AS product_id, 
+    IF(ISNULL(t2.price), 10, t2.price) AS price 
+FROM 
+    (SELECT DISTINCT product_id 
+     FROM products) AS t1 
+LEFT JOIN 
+    (SELECT 
+         product_id, 
+         new_price AS price 
+     FROM 
+         products 
+     WHERE 
+         (product_id, change_date) IN 
+         (SELECT 
+              product_id, 
+              MAX(change_date) 
+          FROM 
+              products 
+          WHERE 
+              change_date <= '2019-08-16' 
+          GROUP BY 
+              product_id)
+    ) AS t2 
+ON 
+    t1.product_id = t2.product_id;
 
-SELECT t1.product_id                      AS product_id, 
-       IF(Isnull(t2.price), 10, t2.price) AS price 
-FROM   (SELECT DISTINCT product_id 
-        FROM   products) AS t1 
-       left join (SELECT product_id, 
-                         new_price AS price 
-                  FROM   products 
-                  WHERE  ( product_id, change_date ) IN (SELECT product_id, 
-                                                                Max(change_date) 
-                                                         FROM   products 
-                                                         WHERE change_date <= '2019-08-16' 
-                                                         GROUP  BY product_id)) 
-                 AS t2 
-              ON t1.product_id = t2.product_id