In SQL, the LAST_VALUE function is used to retrieve the last value in a specified column within a window frame. This function can be further enhanced by using the ROWS BETWEEN clause, which allows you to define the range of rows to consider when applying the LAST_VALUE function.

Here’s an example to demonstrate how to use LAST_VALUE with the ROWS BETWEEN clause:

SELECT product_name, sale_date, quantity,
       LAST_VALUE(quantity) OVER (PARTITION BY product_name
                                  ORDER BY sale_date
                                  ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS last_quantity
FROM sales_table;

In the above code snippet, we are selecting the product_name, sale_date, quantity columns, and using the LAST_VALUE function on the quantity column. The OVER clause is followed by the PARTITION BY clause, which divides the data into partitions based on the product_name column. The ORDER BY clause sorts the partitions by the sale_date column.

The ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW specifies the range of rows to consider for the LAST_VALUE function. In this case, it includes all the rows from the start of the partition up to the current row.

The result of this query will include an additional column called last_quantity, which contains the last value of the quantity column within each partition.

By using the ROWS BETWEEN clause, you have the flexibility to modify the range of rows according to your specific requirements. For instance, you could change it to ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING to consider the previous and next row along with the current row.

#SQL #WindowFunctions

Using LAST_VALUE with the ROWS BETWEEN clause provides a powerful way to obtain the last value of a column within a specified range of rows. Whether you need to track the last transaction, inventory levels, or any other data point, this SQL feature can be quite handy.