Merge pull request #86 from remy727/1251-average-selling-price

1251. Average Selling Price

Author: remy727

README.md

@@ -385,6 +385,7 @@
 | 620 | Not Boring Movies | [MySQL](./database/0620-not-boring-movies.sql) | Easy |
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 | 1148 | Article Views I | [MySQL](./database/1148-article-views-i.sql) | Easy |
+| 1251 | Average Selling Price | [MySQL](./database/1251-average-selling-price.sql) | Easy |
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database/1251-average-selling-price.sql

@@ -0,0 +1,78 @@
+-- 1251. Average Selling Price
+-- Easy
+-- https://leetcode.com/problems/average-selling-price
+
+/*
+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 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     |
++---------------+---------+
+There is no primary key for this table, it may contain duplicates.
+Each row of this table indicates the date, units, and product_id of each product sold. 
+
+Write an SQL query to find the average selling price for each product. average_price should be rounded to 2 decimal places.
+Return the result table in any order.
+The query 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
+*/
+
+SELECT
+	UnitsSold.product_id,
+	ROUND(SUM(UnitsSold.units * Prices.price) / SUM(UnitsSold.units), 2) AS average_price
+FROM
+	UnitsSold
+JOIN
+	Prices
+ON
+	UnitsSold.product_id = Prices.product_id
+	AND UnitsSold.purchase_date BETWEEN Prices.start_date AND Prices.end_date
+GROUP BY
+	UnitsSold.product_id;