Скачать или смотреть How to Sum SQL Aggregate Function Results in PostgreSQL

Learn how to perform operations on aggregate function results in SQL using PostgreSQL with this step-by-step guide.
---
This video is based on the question https://stackoverflow.com/q/69025399/ asked by the user 'Hussnain_Root' ( https://stackoverflow.com/u/16811997/ ) and on the answer https://stackoverflow.com/a/69025505/ provided by the user 'MarEll' ( https://stackoverflow.com/u/11900948/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: i have used sql aggregate function and it has returned me some value and i want to perform opertion on that value

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Summing SQL Aggregate Function Results in PostgreSQL

When working with SQL, particularly with PostgreSQL, you might find yourself needing to perform additional operations on the results of aggregate functions. In this post, we’ll address the common challenge of how to take a summed population by continent and consolidate it into a single record.

The Challenge

You may have executed a query that gives you a breakdown of populations separated by continent, as shown below:

[[See Video to Reveal this Text or Code Snippet]]

This query sums the population grouped by continent, giving you a unique population total for each continent. However, you may want to sum all those totals into one single record, providing you with an overall view of the population across all continents. How can this be achieved?

The Solution

You can accomplish this by utilizing a subquery. Let’s break down the solution step by step.

1. Understand the Subquery

Instead of directly calculating a sum on the initial query, you treat it as a subquery. This allows you to use the results of the original aggregate function in a second query.

2. Construct the Subquery

To sum the all_population results further, you can nest the previous query inside another SELECT statement. Here’s how you’ll do it:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

The SELECT DISTINCT statement gathers unique records for continent while summing their populations.

The subquery is encapsulated (named subquery), allowing it to be referenced in the outer query.

In the outer query, SUM(all_population) is applied to get the final total population across all continents.

3. Execute and Review Your Results

After executing the above code, you will receive a single total population value, which consolidates all the previously calculated population figures into an easily digestible format.

Conclusion

By leveraging subqueries in PostgreSQL, you can effectively manipulate and summarize your data from aggregate function results. This method not only simplifies your final output but also enhances the flexibility of your SQL queries.

Feel free to integrate these techniques into your SQL operations to get the most out of your data analysis tasks!