Upload 142

Author: ggeerraarrdd

README.md

@@ -174,6 +174,7 @@ The problems and both submitted and site solutions are documented in individual
 | 139   | [Second Highest Salary](https://leetcode.com/problems/second-highest-salary/description/)                                                                     | [Solution](solutions/139_second_highest_salary.md)                                    | LeetCode    | Medium       |                                                                     |
 | 140   | [Group Sold Products By The Date](https://leetcode.com/problems/group-sold-products-by-the-date/description/)                                                 | [Solution](solutions/140_group_sold_products_by_the_date.md)                          | DataLemur   | Easy         | `GROUP_CONCAT()`                                                    |
 | 141   | [List the Products Ordered in a Period](https://leetcode.com/problems/list-the-products-ordered-in-a-period/)                                                 | [Solution](solutions/141_list_the_products_ordered_in_a_period.md)                    | DataLemur   | Easy         |                                                                     |
+| 142   | [Product Price at a Given Date](https://leetcode.com/problems/product-price-at-a-given-date/description/)                                                     | [Solution](solutions/142_product_price_at_a_given_date.md)                            | LeetCode    | Medium       | `UNION ALL`, `LEFT JOIN`, Window Function                           |
 <!-- Index End - WARNING: Do not delete or modify this markdown comment. -->
 
 ## Author(s)

solutions/142_product_price_at_a_given_date.md

@@ -0,0 +1,144 @@
+# SQL Everyday \#142
+
+## Product Price at a Given Date
+
+Site: LeetCode\
+Difficulty per Site: Medium
+
+## Problem
+
+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*. [[Full Description](https://leetcode.com/problems/product-price-at-a-given-date/description/)]
+
+## Submitted Solution
+
+```sql
+-- Submitted Solution
+# Write your MySQL query statement below
+
+WITH cte1 AS (
+    SELECT
+        DISTINCT product_id
+    FROM Products
+),
+cte2 AS (
+    SELECT
+        product_id
+        ,MAX(change_date) AS change_date
+    FROM Products
+    WHERE change_date <= '2019-08-16'
+    GROUP BY product_id
+)
+SELECT
+    p1.product_id
+    ,COALESCE(p3.new_price, 10) AS price
+FROM cte1 AS p1
+LEFT JOIN cte2 AS p2 ON p1.product_id = p2.product_id
+LEFT JOIN Products AS p3 ON p2.product_id = p3.product_id AND p2.change_date = p3.change_date
+;
+```
+
+## Site Solution
+
+```sql
+-- LeetCode Solution 
+-- Solution #1: Divide cases by using `UNION ALL`
+SELECT
+  product_id,
+  10 AS price
+FROM
+  Products
+GROUP BY
+  product_id
+HAVING
+  MIN(change_date) > '2019-08-16'
+UNION ALL
+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
+  )
+
+-- Solution #2: Divide cases by using `LEFT JOIN`
+SELECT
+  UniqueProductId.product_id,
+  IFNULL (LastChangedPrice.new_price, 10) AS price
+FROM
+  (
+    SELECT DISTINCT
+      product_id
+    FROM
+      Products
+  ) AS UniqueProductIds
+  LEFT JOIN (
+    SELECT
+      Products.product_id,
+      new_price
+    FROM
+      Products
+      JOIN (
+        SELECT
+          product_id,
+          MAX(change_date) AS change_date
+        FROM
+          Products
+        WHERE
+          change_date <= "2019-08-16"
+        GROUP BY
+          product_id
+      ) AS LastChangedDate USING (product_id, change_date)
+    GROUP BY
+      product_id
+  ) AS LastChangedPrice USING (product_id)
+
+-- Solution #3: Use the window function
+SELECT
+  product_id,
+  IFNULL (price, 10) AS price
+FROM
+  (
+    SELECT DISTINCT
+      product_id
+    FROM
+      Products
+  ) AS UniqueProducts
+  LEFT JOIN (
+    SELECT DISTINCT
+      product_id,
+      FIRST_VALUE (new_price) OVER (
+        PARTITION BY
+          product_id
+        ORDER BY
+          change_date DESC
+      ) AS price
+    FROM
+      Products
+    WHERE
+      change_date <= '2019-08-16'
+  ) AS LastChangedPrice USING (product_id);
+```
+
+## Notes
+
+TBD
+
+## NB
+
+`UNION ALL`, `LEFT JOIN`, Window Function
+
+Go to [Index](../?tab=readme-ov-file#index)\
+Go to [Overview](../?tab=readme-ov-file)
+