In SQL, the LAST_VALUE function allows you to retrieve the last value in a set of rows based on a specified order. This function can be used in combination with conversion functions to manipulate the retrieved value. In this blog post, we will explore how to use LAST_VALUE with conversion functions to perform various transformations on the result.

Basic Usage of LAST_VALUE

The basic syntax of LAST_VALUE is as follows:

LAST_VALUE(expression) OVER (ORDER BY column [ASC|DESC])

Let’s assume we have a table called employees, with the following structure:

To retrieve the last salary from the employees table, we can use the following query:

SELECT LAST_VALUE(Salary) OVER (ORDER BY ID) AS LastSalary
FROM employees;

The result of this query will be:

Since we did not specify a window frame, the LAST_VALUE function considers all rows in the ordered result set.

Converting the Result with Conversion Functions

Conversion functions in SQL can be used to transform the retrieved value from one data type to another. This can be helpful when you need to perform calculations or comparisons with the last value.

Let’s say we want to retrieve the last salary as a percentage of the maximum salary in the employees table. We can achieve this by using the LAST_VALUE function with the MAX function and a conversion function such as CAST:

SELECT CAST(LAST_VALUE(Salary) OVER (ORDER BY ID) AS DECIMAL) / CAST(MAX(Salary) OVER () AS DECIMAL) * 100 AS LastSalaryPercentage
FROM employees;

The result of this query will be:

In this example, we first convert the last salary and maximum salary to decimal data types using the CAST function. Then we perform the calculation to determine the percentage.

Conclusion

The LAST_VALUE function in SQL, combined with conversion functions, allows you to retrieve the last value in a set of rows and manipulate it in various ways. This can be particularly useful when you need to perform calculations, comparisons, or transformations on the last value.