SQL Cumulative Sum

Galaxy Glossary

How do you calculate a running total or cumulative sum in SQL?

Cumulative sum, or running total, calculates a sum of values up to a given point in a dataset. This is useful for tracking trends and analyzing changes over time. SQL provides various methods to achieve this.

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Description

Calculating cumulative sums in SQL is a common task, particularly when analyzing time-series data or tracking progress. The core idea is to add up values sequentially, accumulating the total at each step. This differs from a simple SUM function, which calculates the total of all values in a column. Several approaches can achieve this, each with its own strengths and weaknesses. One common method involves using window functions, which allow calculations across a set of rows related to the current row. Another approach uses self-joins, which can be more complex but offer flexibility in handling specific conditions. Understanding the nuances of these methods is crucial for effective data analysis.

Why SQL Cumulative Sum is important

Cumulative sums are critical for trend analysis, sales forecasting, and monitoring performance over time. They provide a clear picture of how values accumulate, enabling better decision-making based on observed patterns.

Example Usage


-- Example using MySQL DATE_FORMAT
SELECT DATE_FORMAT(order_date, '%m/%d/%Y') AS formatted_date
FROM orders
WHERE customer_id = 1;

-- Example using PostgreSQL to_char
SELECT to_char(order_date, 'MM/DD/YYYY') AS formatted_date
FROM orders
WHERE customer_id = 1;

Common Mistakes

Forgetting to specify the `ORDER BY` clause when using window functions, leading to incorrect cumulative sums.
Using a simple `SUM()` function without window functions, which will only give the total sum, not the cumulative sum.
Incorrectly partitioning the data, resulting in cumulative sums calculated across the entire dataset instead of within specific groups.

SQL Cumulative Sum

How do you calculate a running total or cumulative sum in SQL?

Description

Why SQL Cumulative Sum is important

Example Usage

Common Mistakes

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