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Learn how to troubleshoot and resolve illegal XML character errors when parsing XML columns in SQL Server. Techniques for identifying problematic rows included!
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Resolving Illegal XML Character Errors in SQL Server Parsing

When working with XML data in SQL Server, you might encounter frustrating errors that halt your parsing process. One common issue is the illegal XML character error, which occurs when your SQL code attempts to parse an invalid character in the XML content. This can especially be problematic when processing large data sets, as it can prevent you from extracting the necessary information.

In this guide, we will explore the steps to diagnose and resolve this error effectively, enabling you to continue parsing your XML data without interruptions.

Understanding the Error

What Causes the Illegal Character Error?

The error message typically looks like this:

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

This indicates that the XML parser has encountered a character that is not valid within XML syntax. The parsing failure isn't linked to a particular column of your XML data but often points to the structure or content of the XML itself.

In your case, the SQL command was able to parse a significant number of rows (570,000) before it hit a problematic row that contains an illegal character.

Steps to Resolve the Error

1. Identifying the Problematic Rows

You need a way to identify which rows contain illegal XML characters. Fortunately, SQL Server provides a method to do this using the TRY_CAST function. The following SQL query can help you pinpoint rows that are causing issues:

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

Explanation:

The TRY_CAST function attempts to convert EventXml to an XML data type. If it fails (due to an illegal character), it returns NULL.

The query will return any rows where this conversion fails, effectively isolating the problematic entries.

2. Skipping the Offending Rows

Once you identify the rows with illegal XML characters, you have options on how to handle them:

Exclude the rows: If it's feasible for your analysis, you can modify your initial SQL query to skip over any rows with illegal XML characters.

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

This modification ensures that you only parse valid XML entries, allowing your script to run smoothly without interruption.

3. Cleaning the Data (Optional)

If consistent errors arise due to certain illegal characters or formatting issues, it may be worth cleaning the XML data to address these problems. This can be done programmatically, or through data manipulation techniques prior to insertion or parsing.

Conclusion

Encountering an illegal XML character error can be a significant roadblock when working with XML data in SQL Server. By leveraging the TRY_CAST function, you can effectively identify and filter out rows causing these issues, ensuring that your parsing operations can continue uninterrupted.

By adopting these practical steps, you'll be able to work more efficiently with XML data in SQL Server and reduce the likelihood of running into similar errors in the future. Happy parsing!