Скачать или смотреть How to Handle Empty XML Nodes in SQL Server 2019 with T-SQL

Learn how to efficiently manage empty XML nodes when parsing HTML tables in SQL Server 2019 using T-SQL, and ensure your data returns accurately.
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Handling Empty XML Nodes in SQL Server 2019

When working with XML in SQL Server, especially when parsing HTML, you may encounter challenges with empty nodes that can affect your results. This guide will address a common issue where an empty <td> node can lead to unexpected null values in your query results.

The Problem

Consider a situation where you have an HTML table structure in a string format that includes some empty <td> tags. After stripping out HTML tags and converting it into XML, you may find that querying this XML leads to unexpected behavior — specifically, columns that should contain null values appear as missing or not populated correctly.

Sample HTML Input

Here’s an example of an HTML string that includes an empty <td>:

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

Expected Results

From the above table, here is what we expect:

FieldName should retrieve the first column value.

OldValue should be null since the <td> is empty.

NewValue should retrieve the third column value.

The Solution

To achieve desired results and handle empty nodes correctly, you can slightly modify your T-SQL code. Here’s how:

Step 1: Update Your SELECT Query

By adjusting your query to target the <td> nodes more effectively, you can get around the issue with empty values. Here’s the revised T-SQL query:

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

Explanation of Changes

Node Targeting: We removed the /table from the path and directly accessed the <tr> nodes. This approach simplifies the selection and ensures that we are directly querying the rows individually.

Handling Empty Nodes: By selecting the value of the second <td> without specifying text(), SQL Server will return NULL for the empty node rather than missing data.

Result Verification

After implementing the updated query, execute it against your data and expect the following output:

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

Conclusion

With these modifications, your T-SQL query now effectively handles scenarios with empty XML nodes. This ensures that your results represent the actual structure of your HTML table, allowing you to manage your data with greater accuracy in SQL Server 2019.

By understanding how to navigate the intricacies of XML and T-SQL, you can better parse and analyze your data effectively.