Solved -> 1164. Product Price at a Given Date

Author: NandiSoham

05_Avanced_Select_and_Joins/Q_05-1164. Product Price at a Given Date.sql

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+/* 
+
+Problem Link -> https://leetcode.com/problems/product-price-at-a-given-date/description/?envType=study-plan-v2&envId=top-sql-50
+
+------------------------------------------------------------- QUESTION -----------------------------------------------------------
+
+Table: Products
+
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| product_id    | int     |
+| new_price     | int     |
+| change_date   | date    |
++---------------+---------+
+(product_id, change_date) is the primary key (combination of columns with unique values) of this table.
+Each row of this table indicates that the price of some product was changed to a new price at some date.
+ 
+
+Write a solution to find the prices of all products on 2019-08-16. Assume the price of all products before any change is 10.
+Return the result table in any order.
+The result format is in the following example.
+
+
+Example 1:
+
+Input: 
+Products table:
++------------+-----------+-------------+
+| product_id | new_price | change_date |
++------------+-----------+-------------+
+| 1          | 20        | 2019-08-14  |
+| 2          | 50        | 2019-08-14  |
+| 1          | 30        | 2019-08-15  |
+| 1          | 35        | 2019-08-16  |
+| 2          | 65        | 2019-08-17  |
+| 3          | 20        | 2019-08-18  |
++------------+-----------+-------------+
+
+Output: 
++------------+-------+
+| product_id | price |
++------------+-------+
+| 2          | 50    |
+| 1          | 35    |
+| 3          | 10    |
++------------+-------+
+
+*/
+
+-- ----------------------------------------------------------- SOLUTION -----------------------------------------------------------
+
+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
+)
+UNION
+SELECT product_id, 10 AS price
+FROM Products
+WHERE product_id NOT IN
+(
+    SELECT product_id
+    FROM Products
+    WHERE change_date <= '2019-08-16'
+)
+