How to fix Error 572 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 572 – “Invalid Regular Expression”

Why This Error Happens

Error 572 occurs when SQL Server 2025’s native regular expression functions (such as REGEXP_LIKE, REGEXP_REPLACE, or REGEXP_MATCHES) receive a pattern string that does not conform to the supported regex syntax subset. This is typically caused by unescaped special characters, unsupported syntax carried over from other regex engines (like PCRE or .NET-specific lookaheads), or a malformed pattern generated dynamically by application code. In some cases, the issue stems from collation or encoding mismatches that corrupt the pattern string before it reaches the parser.

Step-by-Step Resolution Guide

Step 1: Isolate the Offending Query and Pattern

  • Capture the exact query using SQL Server Profiler or Extended Events, filtering on Error Number = 572.
  • Note the offset value reported in the error message — this points to the exact character position in the pattern causing the failure.
  • Run the query in SSMS manually to reproduce the error outside the application layer.

Step 2: Validate and Correct the Regex Syntax

  • Cross-reference the pattern against Microsoft’s documented supported regex grammar for SQL Server 2025 (a restricted subset, not full PCRE).
  • Escape special characters correctly — particularly backslashes, brackets [ ], and parentheses ( ), which often require double-escaping in T-SQL string literals.
  • Remove unsupported constructs such as lookbehind (?<=...), named capture groups, or inline flags (?i), none of which are supported natively.
  • Example fix: replace '\d{3}-\d{4}' issues by testing with SELECT REGEXP_LIKE('123-4567', '\d{3}-\d{4}') in isolation.

Step 3: Check Collation and Encoding Settings

  • Verify the database collation using:
SELECT DATABASECOLLATION FROM sys.databases WHERE name = 'YourDBName';
  • Ensure the connection and column collation match, particularly for Unicode (NVARCHAR) columns feeding into the regex function.
  • If patterns are stored in a table or passed from an app, confirm no invisible characters (BOM, non-breaking spaces) are being inserted.

Step 4: Update SQL Server 2025 Cumulative Updates

  • Confirm the instance is on the latest Cumulative Update (CU) via:
SELECT @@VERSION;
  • Apply the latest CU from the Microsoft Update Catalog, as early regex engine builds in SQL Server 2025 had known parser bugs with nested quantifiers.
  • Restart the SQL Server service via services.msc or net stop MSSQLSERVER && net start MSSQLSERVER after patching.

Step 5: Rebuild Dynamic Pattern Generation Logic

  • If patterns are built dynamically in application code (C#, Python, etc.), log the final constructed string before it’s sent to SQL Server.
  • Add server-side validation using TRY_CAST or a wrapper stored procedure that tests the pattern with a dummy string before executing it against production data.

Alternative or Verification Steps

  • Verify the fix: Re-run the isolated query from Step 1 in SSMS and confirm it returns results without throwing Error 572; then re-test the full application workflow end-to-end.
  • Alternative approach: If the pattern requires advanced regex features unsupported by SQL Server’s engine, offload the regex evaluation to a CLR function or handle the matching logic in the application layer instead of T-SQL.