In SQL, the LAST_VALUE function is used to return the last value in a sorted group of rows. This function can be very useful in scenarios where you have multiple rows with the same value and you want to retrieve the latest one based on some criteria.

However, there may be cases where you need to use the LAST_VALUE function within a subquery to achieve more complex results. In this blog post, we will explore how to use the LAST_VALUE function with a subquery in SQL.

Scenario

Let’s consider a scenario where we have a table called sales with the following structure:

CREATE TABLE sales (
    sale_id INT,
    product_id INT,
    sale_date DATE,
    quantity INT,
    price DECIMAL(10,2)
);

We want to retrieve the latest sale price for each product based on the sale date. To achieve this, we can use the LAST_VALUE function within a subquery.

Solution

To get the latest sale price for each product, we can follow these steps:

1. Write a subquery to group the rows by product and sort them by the sale date in descending order.

   SELECT product_id, sale_date, price
   FROM (
       SELECT product_id, sale_date, price, 
       ROW_NUMBER() OVER (PARTITION BY product_id ORDER BY sale_date DESC) AS row_num
       FROM sales
   ) AS subquery
   WHERE row_num = 1;
   

   In this subquery, we are using the ROW_NUMBER function to assign a row number to each row within the same product group, ordered by the sale date in descending order. We then filter only the rows with row_num = 1 to get the latest sale for each product.

2. Use the subquery with the LAST_VALUE function to retrieve the latest sale price for each product.

   SELECT product_id, LAST_VALUE(price) OVER (PARTITION BY product_id ORDER BY sale_date DESC) AS last_sale_price
   FROM (
       SELECT product_id, sale_date, price, 
       ROW_NUMBER() OVER (PARTITION BY product_id ORDER BY sale_date DESC) AS row_num
       FROM sales
   ) AS subquery
   WHERE row_num = 1;
   

   In this query, we are using the LAST_VALUE function to retrieve the last sale price for each product, based on the sale date order within the product group.

Conclusion

Using the LAST_VALUE function with a subquery can be quite powerful in SQL when you need to retrieve the last value from a sorted group of rows. In this blog post, we have explored how to use the LAST_VALUE function with a subquery to retrieve the latest sale price for each product based on the sale date.