In SQL, the LAST_VALUE function can be used to retrieve the last value in a specific column or expression within a result set. However, when using date functions in conjunction with LAST_VALUE, there are a few important considerations to keep in mind.

Let’s say we have a table named orders with the following structure:

We want to find the last order date using the LAST_VALUE function and perform some calculations on the result.

Syntax

The basic syntax for using LAST_VALUE in SQL is as follows:

SELECT LAST_VALUE(column/expr) OVER (ORDER BY ordering_clause)
FROM table_name

In our case, we want to retrieve the last order date, so the syntax would be:

SELECT LAST_VALUE(order_date) OVER (ORDER BY order_date) AS last_order_date
FROM orders

However, using this query directly would return the same order date for each row, which is not what we desire. To make use of date functions, we need to modify the query slightly.

Incorporating Date Functions

To incorporate date functions with the LAST_VALUE function, we can use a subquery or a Common Table Expression (CTE). Let’s use a subquery as an example:

SELECT LAST_VALUE(order_date) OVER () AS last_order_date
FROM (
    SELECT order_date
    FROM orders
    ORDER BY order_date DESC
    LIMIT 1
) subquery

In the above query:

• The subquery selects the order_date column from the orders table and orders it in descending order.
• The LAST_VALUE function is used without any specific ORDER BY clause in the window function.
• Finally, the LAST_VALUE result is assigned an alias last_order_date.

By using the subquery, we first order the data in descending order and then select the last value using LAST_VALUE.

Conclusion

By incorporating date functions, we can accurately retrieve the last value in a column using the SQL LAST_VALUE function. Whether using a subquery or a CTE, correct ordering of the data is crucial to get the desired result.