How to fix Error 452 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 452 – COLLATE Clause Cannot Be Used on User-Defined Data Types

Why This Error Happens

This error occurs because SQL Server does not permit the COLLATE clause to be applied directly to columns defined with a user-defined data type (UDT/alias type). Collation is inherited from the base data type at the time the UDT was created, so attempting to override it in a CREATE TABLE or ALTER TABLE statement is rejected. This is commonly seen when scripts are migrated from older databases or generated by tools that append a COLLATE clause universally, without checking whether the target column uses a system type or a custom alias type.

Step-by-Step Resolution Guide

Step 1: Identify the User-Defined Data Type in the Script

  • Open the failing T-SQL script in SQL Server Management Studio (SSMS) connected to your Windows Server 2025 instance.
  • Locate the column definition triggering Error 452 (it will reference a custom type, e.g., dbo.MyCustomString).
  • Run the following query to confirm the type is user-defined:
  SELECT name, is_user_defined 
  FROM sys.types 
  WHERE name = 'MyCustomString';

Step 2: Remove or Relocate the COLLATE Clause

  • Edit the script and delete the COLLATE clause from the column that uses the user-defined type.
  • Example of the invalid syntax:
  CREATE TABLE dbo.Test (
      Col1 dbo.MyCustomString COLLATE SQL_Latin1_General_CP1_CI_AS
  );
  • Corrected syntax (remove COLLATE entirely, since it’s inherited):
  CREATE TABLE dbo.Test (
      Col1 dbo.MyCustomString
  );

Step 3: Modify the Base Type’s Collation (If a Different Collation Is Required)

  • If a different collation is genuinely needed, you must drop and recreate the user-defined type with the desired collation on its base type.
  • Run:
  DROP TYPE dbo.MyCustomString;
  GO
  CREATE TYPE dbo.MyCustomString 
      FROM NVARCHAR(50) COLLATE French_CI_AS;
  GO
  • Ensure no existing tables reference the old type before dropping it; otherwise, SQL Server will block the DROP TYPE operation with a dependency error.

Step 4: Re-run the Script and Validate Dependent Objects

  • Execute the corrected CREATE TABLE or ALTER TABLE script.
  • Check for any stored procedures, views, or functions that referenced the old type definition and recompile them if needed:
  EXEC sp_refreshsqlmodule 'dbo.YourProcedureName';

Alternative or Verification Steps

  • Verify the fix by querying sys.columns and sys.types to confirm the column now correctly inherits the collation from its base type without triggering Error 452 on script execution.
  • If altering the UDT is not feasible due to widespread dependencies, consider changing the column to use the native base type (e.g., NVARCHAR(50)) directly in the table definition, applying COLLATE there instead of on the alias type.