@@ -1,3 +1,80 @@
+-- Problem:
+
+/*
+Table: Prices
+
++---------------+---------+
+| Column Name | Type |
++---------------+---------+
+| product_id | int |
+| start_date | date |
+| end_date | date |
+| price | int |
++---------------+---------+
+(product_id, start_date, end_date) is the primary key (combination of columns with unique values) for this table.
+Each row of this table indicates the price of the product_id in the period from start_date to end_date.
+For each product_id there will be no two overlapping periods. That means there will be no two intersecting periods for the same product_id.
+
+
+Table: UnitsSold
+
++---------------+---------+
+| Column Name | Type |
++---------------+---------+
+| product_id | int |
+| purchase_date | date |
+| units | int |
++---------------+---------+
+This table may contain duplicate rows.
+Each row of this table indicates the date, units, and product_id of each product sold.
+
+
+Write a solution to find the average selling price for each product. average_price should be rounded to 2 decimal places. If a product does not have any sold units, its average selling price is assumed to be 0.
+
+Return the result table in any order.
+
+The result format is in the following example.
+
+
+
+Example 1:
+
+Input:
+Prices table:
++------------+------------+------------+--------+
+| product_id | start_date | end_date | price |
++------------+------------+------------+--------+
+| 1 | 2019-02-17 | 2019-02-28 | 5 |
+| 1 | 2019-03-01 | 2019-03-22 | 20 |
+| 2 | 2019-02-01 | 2019-02-20 | 15 |
+| 2 | 2019-02-21 | 2019-03-31 | 30 |
++------------+------------+------------+--------+
+UnitsSold table:
++------------+---------------+-------+
+| product_id | purchase_date | units |
++------------+---------------+-------+
+| 1 | 2019-02-25 | 100 |
+| 1 | 2019-03-01 | 15 |
+| 2 | 2019-02-10 | 200 |
+| 2 | 2019-03-22 | 30 |
++------------+---------------+-------+
+Output:
++------------+---------------+
+| product_id | average_price |
++------------+---------------+
+| 1 | 6.96 |
+| 2 | 16.96 |
++------------+---------------+
+Explanation:
+Average selling price = Total Price of Product / Number of products sold.
+Average selling price for product 1 = ((100 * 5) + (15 * 20)) / 115 = 6.96
+Average selling price for product 2 = ((200 * 15) + (30 * 30)) / 230 = 16.96
+*/
+
+-------------------------------------------------------------------------------
+
+-- Solution:
+
 SELECT p.product_id,ROUND(IFNULL(SUM(u.units * p.price)/SUM(u.units),0),2) AS average_price FROM Prices p
 LEFT JOIN UnitsSold u ON p.product_id = u.product_id AND u.purchase_date BETWEEN p.start_date AND p.end_date
 GROUP BY p.product_id