Cumulative totals are a common requirement when analyzing data, especially in finance or sales. Calculating cumulative totals involves summing up a value repeatedly, as each row is processed.

One way to achieve this in SQL is by using the FIRST_VALUE() function. This function allows us to access the value of a specified column from the first row of a partition.

Let’s consider a table sales with the following schema:

CREATE TABLE sales (
    date DATE,
    amount INT
);

To calculate the cumulative sales amount for each date, we can use the following query:

SELECT
    date,
    SUM(amount) OVER (
        ORDER BY date
        ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    ) AS cumulative_total
FROM sales;

In this query, we use the SUM() function along with the OVER clause. The ORDER BY date ensures that the calculation is done in ascending order of dates. The ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW clause specifies that we want the sum from the first row up to the current row.

The FIRST_VALUE() function is implicitly used here when we specify ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW. It fetches the value of amount from the first row within the partition (all rows in this case) for each row.

The result of the query would be a result set with the date and the cumulative total for each date.

For example:

By utilizing the FIRST_VALUE() function and the OVER clause with the appropriate ROWS BETWEEN specification, we can easily calculate cumulative totals in SQL.

This technique can be extended to perform various calculations and analysis on cumulative data, such as identifying peaks, trends, or forecasting.

References

• Oracle Documentation on FIRST_VALUE
• Microsoft SQL Server Documentation on FIRST_VALUE