Product Price at a Given Date SQL MySQL leetcode solution with common table expression and join
Product Price at a Given Date SQL MySQL leetcode solution with common table expression and join
Challenge: Finding Product Prices on a Specific Date
Difficulty: Medium
Data:
A table named Products stores product price change history:
product_id (int): Unique identifier for each product.
new_price (int): The updated price for the product.
change_date (date): The date the price change took effect.
(product_id, change_date) is the primary key (unique combination).
Objective:
Given a specific date, find the price of each product as of that date. Assume the initial price for all products is 10 before any changes are recorded in the table.
Output:
A table with two columns:
product_id (int): The unique identifier for each product.
price (int): The price of the product on the specified date.
Explanation:
We need to query the Products table considering two things:
Price Changes: Identify the latest price change for each product before the given date.
Initial Price: If there's no recorded price change before the given date for a product, assume its price is 10 (the initial price).
Here are two common approaches to achieve this:
Approach 1: Using MAX with a Subquery:
Use a subquery to find the maximum change_date that's less than or equal to the given date for each product.
In the main query, join the Products table with the subquery result to get the latest price change record before the given date (if any).
Use a CASE statement to handle products with no price change records before the given date (set their price to 10).
This approach leverages a subquery and a join to find the relevant product prices for the given date.
Subquery:
We create a subquery that finds the maximum change_date for each product_id that's less than or equal to the given date (2019-08-16). This essentially identifies the latest price change record before the target date for each product.
Join:
We join the Products table with the result of the subquery on both product_id and change_date. This ensures we retrieve the price corresponding to the latest change date identified in the subquery.
Handling Missing Records:
A CASE statement is used to address products with no price change record before the given date. If there's no matching record in the join (meaning the subquery didn't find a relevant price change), the price is set to the assumed initial price (10).
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