How to Aggregate Query Results in PostgreSQL Using Knex.js

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The Problem

Suppose you have the following tables which are interconnected:

Houses: This table has the columns id, title, city, and country.

Images: This table contains id, name, and house_id (which is a foreign key referencing the Houses table).

You may write a query to join these tables like so:

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

The above query will return data like this:

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

As you can see, the result is repetitive concerning the house details, which is not optimal. You would likely prefer a cleaner structure, such as this:

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

The Solution

To achieve this cleaner output, you need to group the results by the unique house parameters and aggregate the image names.

Step-by-Step Explanation

Group By: Use the GROUP BY statement to define which columns you want to group by. In this case, you will group all the columns that make each house unique.

Aggregate the Image Names: Use the array_agg() function to gather all associated image names into a single array for each unique house.

Here’s how you can modify your SQL query:

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

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

Key Takeaways

Grouping your results and aggregating data can transform repetitive entries into a more structured and readable format.

Using array_agg in PostgreSQL is powerful in collecting related data into a single array.

Now, you’ll have a well-organized and concise data structure that enhances data visibility and usability for your applications. Happy coding!