How to Retrieve All Model Names from Nested JSON in SQL Using OPENJSON

Discover how to extract a list of models from nested JSON data in SQL using the `OPENJSON` function, particularly when it returns NULL.
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How to Retrieve All Model Names from Nested JSON in SQL Using OPENJSON

When working with JSON data in SQL Server, one common challenge developers face is effectively querying nested structures. In this article, we will explore a specific scenario where users encounter issues retrieving model names from a JSON object that contains several layers of nested arrays.

The Problem

The main issue at hand is with a JSON structure similar to the following:

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

The Challenge

When attempting to write a SQL query using OPENJSON to extract all model names directly, issues arise:

Using a specific index (e.g., Models[0].Make) returns results for only that specific model.

When trying to access just Models.Make, it yields NULL results.

The objective is to extract a comprehensive list of models irrespective of their makes.

The Solution

To retrieve all model names effectively, we can utilize the CROSS APPLY method alongside OPENJSON. This method helps in navigating through the nested arrays.

Step-by-Step Query Breakdown

Here is the SQL code that accomplishes this:

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

Explanation of the Query:

Main JSON Object: OPENJSON(@ PermsJSON, '$.Models') retrieves the array of Models.

Nested Structures: The first CROSS APPLY retrieves the Make for each Model.

Final Extraction: The second CROSS APPLY drills down into the Models array under each Make, allowing us to fetch the individual model names.

Results

When executed, the above query returns a list like this:

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

Conclusion

By using OPENJSON in conjunction with CROSS APPLY, you can effectively navigate through complex, nested JSON structures in SQL Server to extract meaningful data. When faced with issues like receiving NULL results or only partial data, remember this structured approach.

This method not only helps to retrieve the desired output but also enhances your skills in managing JSON data in SQL. Happy querying!