How to Compute a Running Total in MySQL

Computing running totals is a common task that involves calculating the cumulative sum of the values over a specified sequence or range. MySQL a popular relational database management system provides powerful features for performing such computations efficiently.

In this article, we’ll explore how to calculate running totals in MySQL using various techniques and approaches.

A running total also known as a cumulative sum represents the summation of the values as they accumulate over time or a specific sequence. It offers insights into the cumulative progress, growth, or accumulation of the quantity over a period. For instance, in financial applications, the totals are used to track account balances, revenue, expenses, or stock prices over time.

• Using Variables
• Using Subqueries
• Using JOINs

• Using Variables: The MySQL user-defined variables can be leveraged to compute running totals by maintaining a cumulative sum as rows are processed.
• Using Subqueries: The Subqueries can be employed to calculate running totals by summing up values from the preceding rows within the same query.
• Using JOINs: The JOIN operations can be utilized to join a table with itself, allowing for the aggregation of values from the previous rows.
• Using Window Functions: MySQL 8.0 introduced window functions such as the ROW_NUMBER(), PARTITION BY, and ORDER BY which enable the efficient computation of the running totals in a single query.

Example 1: Using Variables

Create your_table:

CREATE TABLE your_table (
    id INT AUTO_INCREMENT PRIMARY KEY,
    value INT
);
INSERT INTO your_table (value) VALUES (10), (20), (30), (40), (50);

SET @running_total := 0;
SELECT id, value, (@running_total := @running_total + value) AS running_total
FROM your_table
ORDER BY id;

Output:

Explanation: The output displays the id and value columns from the your_table table, along with a running_total column. The running_total column shows the cumulative sum of value, calculated incrementally by row.

Example 2: Using Subqueries

SELECT id, value, (
    SELECT SUM(value)
    FROM your_table t2
    WHERE t2.id <= t1.id
) AS running_total
FROM your_table t1
ORDER BY id;

Output:

Explanation: The output presents id, value, and running_total. The running_total column accumulates the sum of value up to each row, calculated by summing values with id less than or equal to the current row’s id.

Example 3: Using JOINs

SELECT t1.id, t1.value, SUM(t2.value) AS running_total
FROM your_table t1
JOIN your_table t2 ON t2.id <= t1.id
GROUP BY t1.id, t1.value
ORDER BY t1.id;

Output:

Explanation: The query utilizes a self-join to compute the running total. For each row in your_table, it sums the value column from all rows with IDs less than or equal to the current row’s ID. Results are grouped by id and value, displaying the running total.

In conclusion , MySQL offers effective ways to calculate running totals, which are important for keeping track of progress over time or specific sequences. By using techniques like variables, subqueries, and JOINs, users can easily calculate these totals with flexibility and efficiency. These methods can help users gain insights into various applications, including financial analysis, by accurately calculating cumulative sums. By understanding and applying these techniques, users can perform advanced data analysis tasks in MySQL.