How to fix Error 6874 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: SQL Server Error 6874 – Empty URI in WITH XMLNAMESPACES Clause

Why This Error Happens

This error occurs when a T-SQL query uses the WITH XMLNAMESPACES clause with an empty string ('') as the namespace URI, which SQL Server’s XML parser explicitly disallows. Unlike a default namespace declaration in standard XML (xmlns=""), SQL Server requires that if you declare a default namespace, it must resolve to a non-empty, valid URI value. This is typically caused by dynamically generated SQL, legacy code migrated from an older schema, or a copy-paste error where a namespace variable failed to populate correctly before the query executed.

Step-by-Step Resolution Guide

Step 1: Locate the Offending Query

  • Identify the exact stored procedure, view, or dynamic SQL script triggering Error 6874 using SQL Server Profiler or Extended Events on your SQL Server 2025 instance.
  • Search the query text for the syntax pattern WITH XMLNAMESPACES (DEFAULT '' AS ...) or similar empty-string declarations.
  • Check if the URI value is being passed via a variable (e.g., DECLARE @ns VARCHAR(100) = '') that is failing to initialize.

Step 2: Correct the Namespace Declaration

  • Replace the empty string with a valid, non-null URI. If you only need to strip prefixes for parsing, use a placeholder URI instead of an empty one, such as:
  WITH XMLNAMESPACES (DEFAULT 'http://www.example.com/default' AS ns)
  • If the intention was to remove the namespace from the XML entirely, modify the XML source data to remove the xmlns="" attribute via .modify() before shredding the XML, rather than relying on the query’s WITH clause to handle the empty value.

Step 3: Audit Dynamic SQL and ETL Scripts

  • If the query is generated dynamically (e.g., via SSIS packages or an external application on Windows Server 2025), check the source code logic that concatenates the namespace string.
  • Look for truncation issues or incorrect parsing of the source XML schema that might result in a null or empty variable being injected into the WITH XMLNAMESPACES clause.
  • Update the application logic to validate that the URI variable is not empty before constructing the final T-SQL string.

Step 4: Apply Cumulative Updates

  • Ensure your Microsoft SQL Server 2025 instance is patched with the latest Cumulative Update (CU) via SQL Server Setup, as XML parsing engine behaviors are occasionally refined in these updates.
  • Restart the SQL Server service via services.msc or net stop MSSQLSERVER followed by net start MSSQLSERVER after applying any updates.

Alternative or Verification Steps

  • Verify the Fix: Re-run the specific query in SQL Server Management Studio (SSMS) and confirm the XML shredding/querying operation completes without throwing Error 6874, ensuring the output XML or table result renders correctly.
  • Alternative Approach: If dropping the namespace is not feasible, utilize the nodes() and value() methods with wildcard namespace prefixes (*:) in your XQuery expressions to bypass the need for a strict WITH XMLNAMESPACES declaration altogether.