In SQL, the LAST_VALUE function is used to fetch the last value within a specific window or partition. It is commonly used for time series analysis or when you need to access the last record in a dataset based on a specific ordering.

In this blog post, we will specifically explore how to use LAST_VALUE with a subquery type in SQL. This scenario arises when we want to retrieve the last value from a subquery result set.

Let’s consider the following example of an imaginary table called sales:

CREATE TABLE sales (
    id INT,
    product_id INT,
    sale_date DATE,
    revenue DECIMAL(10,2)
);

Suppose we have data in the sales table as follows:

Now let’s say we want to retrieve the last sale revenue for each product. We can achieve this using the LAST_VALUE function with a subquery type. Here’s an example query:

SELECT DISTINCT
    product_id,
    LAST_VALUE(revenue) OVER (PARTITION BY product_id ORDER BY sale_date 
    ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS last_revenue
FROM
    sales

In the above query, we first order the rows by sale_date within each partition of product_id. Then, we use the LAST_VALUE function with a window frame that includes all rows using ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING. The DISTINCT keyword is used to remove any duplicate results.

The result of the above query would be:

By using LAST_VALUE with a subquery type, we were able to retrieve the last sale revenue for each product.

In conclusion, the LAST_VALUE function in SQL is a useful tool for accessing the last value within a specified window or partition. When combined with a subquery type, it allows us to fetch the last value from a subquery result set, as demonstrated in this blog post.

#SQL #WindowFunctions