1251. Average Selling Price
Description
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
Solutions
Solution 1: Left Join + Grouping
We can use a left join to join the Prices
table and the UnitsSold
table on product_id
, and the condition that purchase_date
is between start_date
and end_date
. Then, we can use GROUP BY
to group by product_id
for aggregation, and use the AVG
function to calculate the average price. Note that if a product has no sales records, the AVG
function will return NULL
, so we can use the IFNULL
function to convert it to $0$.
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