How to Successfully Query XML Documents in SQL Using XQuery

Learn how to extract data from XML documents in SQL using `XQuery` instead of deprecated methods like `OPENXML`. This guide will help you resolve common issues with XML namespaces efficiently.
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Unable to Query XML Document with SQL/OPENXML? Here’s the Solution!

When working with XML files in SQL, you might run into issues querying the data, especially if you haven't considered namespaces properly. If you find yourself facing a situation where your SQL query returns NULL instead of the expected value from your XML file, then this post is for you. Let's break down how to effectively extract data from XML in SQL Server.

The Problem

You have an XML file structured as follows:

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

You are attempting to extract the <mRID> value using the deprecated OPENXML method, but your result returns NULL, indicating that something is amiss. This can often be attributed to the fact that your XML has a default namespace.

The Better Approach: XQuery

Starting from SQL Server 2005, it's recommended to use XQuery for querying XML data because it is more efficient and much better aligned with modern standards than the older OPENXML method. Below are solutions that demonstrate how to extract the <mRID> value correctly using XQuery.

SQL Query from a Variable

If you are testing or running queries directly from an XML variable, use the following approach:

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Explanation

XMLNAMESPACES: This defines the default namespace used in your XML.

SELECT Statement: This retrieves the value of <mRID> using its path and ensures that you extract the text correctly.

SQL Query Directly from an XML File

In case you want to read the XML data directly from a file, here’s how you can format your query:

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

Explanation

Here, you are using OPENROWSET to read the XML file and TRY_CAST to convert it into XML format.

The query then successfully navigates through the XML structure to extract the desired value.

Final Output

When implemented correctly, both of the above methods yield the expected outcome:

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

Conclusion

By transitioning from the deprecated OPENXML method to modern XQuery practices, you can efficiently query XML documents while avoiding common pitfalls such as namespace issues. Always remember to declare namespaces when working with XML, and you will successfully retrieve the values you need. If you encounter similar problems in the future, refer back to these methods to guide you towards a solution.

Happy querying!