In SQL, the LAST_VALUE function is used to retrieve the last value in an ordered set of values. It is commonly used in scenarios where you want to access the most recent value in a specific order. The LAST_VALUE function can be used with other window functions, such as PARTITION BY and ORDER BY, to further refine the results.

Here are a few examples of how to use the LAST_VALUE function in SQL:

Example 1: Retrieve the last value in a column

Suppose you have a table named employees with columns employee_id, name, and salary. You want to find the last (most recent) salary of each employee based on their employee_id. You can use the LAST_VALUE function to achieve this:

SELECT DISTINCT employee_id, 
  LAST_VALUE(salary) OVER (PARTITION BY employee_id ORDER BY employee_id) AS last_salary
FROM employees;

In this example, we use the LAST_VALUE function with the PARTITION BY clause to group the results by employee_id. The ORDER BY clause is used to specify the order in which the values should be considered. The result is a distinct list of employee IDs with their corresponding last salary.

Example 2: Retrieve the last non-null value in a column

Sometimes, you may have a column with null values, and you want to retrieve the last non-null value for each row. The LAST_VALUE function can help you achieve this as well.

SELECT employee_id, name,
  LAST_VALUE(salary IGNORE NULLS) OVER (ORDER BY employee_id) AS last_non_null_salary
FROM employees;

In this example, we use the IGNORE NULLS option with the LAST_VALUE function to skip the null values while determining the last non-null salary. The ORDER BY clause is used to specify the order in which the values should be considered.

Conclusion

The LAST_VALUE function is a powerful tool in SQL to retrieve the last value in a set of ordered values. It is useful in various scenarios, such as finding the most recent value or the last non-null value in a column. By leveraging its capabilities with window functions like PARTITION BY and ORDER BY, you can further fine-tune the results to meet your specific requirements.

#SQL #WindowFunctions