How to Calculate Cumulative Sums in PostgreSQL Using Window Functions?

Calculation of cumulative sum in PostgreSQL

In data processing, it is often necessary to calculate the cumulative sum or running sum of a specific field. In PostgreSQL, this can be easily achieved using window functions.

Introduction to window functions

Window functions allow you to perform calculations on rows grouped together based on specific conditions. In this example, we want to group the rows by circle_id and calculate the cumulative sum of the amount field.

Query to calculate cumulative sum

The following query demonstrates how to calculate the cumulative sum:

SELECT ea_month, id, amount, ea_year, circle_id, sum(amount) OVER (PARTITION BY circle_id ORDER BY ea_year, ea_month) AS cum_amt
FROM tbl
ORDER BY circle_id, ea_year, ea_month;

In this query:

The
• PARTITION BY clause groups rows by circle_id column.
The
• ORDER BY clause sorts the rows in each partition by ea_year and ea_month.
The
• OVER clause defines a window that applies the sum() function to rows starting from each partition to the current row.
• The resulting cumulative sum is stored in the cum_amt column.

Processing date and time data

If your ea_year and ea_month columns are stored as strings, the query will be sorted alphabetically instead of chronologically. To sort correctly, consider converting it to a date type before performing the calculation.

Exclude peers

In PostgreSQL 11 and later, you can use the frame_exclusion option to control how peers are handled in window functions. This allows you to include or exclude certain rows from calculations.

Following these steps, you can efficiently calculate cumulative sums in PostgreSQL, providing valuable insights into your data.

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