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Problem

Table: Products

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| product_id    | int     |
| new_price     | int     |
| change_date   | date    |
+---------------+---------+
(product_id, change_date) is the primary key 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 an SQL query 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 query 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    |
+------------+-------+

Code

select distinct product_id, 10 as price
from Products
group by product_id
having (min(change_date) > "2019-08-16")

union

select p2.product_id, new_price
from Products p2
where (p2.product_id, p2.change_date) in

(
select product_id, max(change_date) as recent_date
from Products
where change_date <= "2019-08-16"
group by product_id
)