How to Flatten Nested JSON Structure in PostgreSQL

Learn how to effectively `flatten nested JSON structures` in PostgreSQL using queries. Get a straightforward solution to extract employee data from your JSON column.
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How to Flatten Nested JSON Structure in PostgreSQL

Working with JSON data can be quite challenging, especially when it comes to nested structures. If you're using PostgreSQL and find yourself needing to extract information from a nested JSON object, you're not alone. In this guide, we'll tackle the specific problem of flattening a nested JSON structure to retrieve employee data from a PostgreSQL database.

Understanding the Problem

Suppose you have a PostgreSQL table that contains a JSON column structured like this:

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

From this structure, you want to extract a list of all the employees present in the employees array. The expected output should look like this:

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

Despite trying various methods, you were unable to retrieve the data using JSON_ARRAY_ELEMENTS. In this blog, we will present a solution that works effectively.

Solution Overview

In PostgreSQL, we can utilize Common Table Expressions (CTEs) along with the jsonb_array_elements and jsonb_array_elements_text functions to flatten the nested structure. Let's break down the solution step by step:

Step 1: Set Up the Table

First, create a table to hold your JSON data:

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

Then, insert the JSON data into the table:

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

Step 2: Extract Employee Data

Now, we'll write a query that extracts the employees using a CTE:

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

Explanation of the Query

CTE Declaration: We begin by defining a CTE called data that selects each record from the JSON array in the records field.

Extraction of Employees: We then use jsonb_array_elements_text to extract each employee from the employees array nested within each emp_file.

Running the Query

When you run this query against your PostgreSQL database, it will yield a result set containing all the employee names extracted from the nested JSON, just as you wanted.

Expected Output

The output of the above query will be:

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

Conclusion

By following the steps outlined above, you should now be able to successfully flatten nested JSON structures in PostgreSQL and extract the needed data. This technique is particularly useful when working with complex data sets where similar structures appear frequently. If you face issues or have any questions, feel free to ask in the comments below!