How to fix Error 4133 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4133

Why This Error Happens

This error occurs when a T-SQL scalar function’s RETURN statement contains an invalid expression, such as a subquery that returns multiple columns, a table variable, or a non-scalar construct instead of a single value. SQL Server 2025’s parser strictly enforces that the RETURN clause in a scalar function must resolve to exactly one scalar value of a compatible data type. This commonly happens after code migrations, schema changes that alter column counts in referenced views, or when a SELECT statement inside the function inadvertently returns a result set rather than a single value.

Step-by-Step Resolution Guide

Step 1: Locate the Offending Function Definition

  • Open SQL Server Management Studio (SSMS) and connect to the instance reporting Error 4133.
  • Run the following query to identify recently modified scalar functions:
  SELECT name, modify_date FROM sys.objects 
  WHERE type = 'FN' ORDER BY modify_date DESC;
  • Script out the function using sp_helptext '<FunctionName>' to inspect the RETURN statement.

Step 2: Correct the RETURN Expression

  • Ensure the expression immediately following RETURN evaluates to a single scalar value (e.g., RETURN @Result; not RETURN (SELECT * FROM Table);).
  • If using a subquery, wrap it to force a single column and row:
  RETURN (SELECT TOP 1 ColumnName FROM TableName WHERE Condition = @Param);
  • Replace any table-valued logic with a declared scalar variable assigned via SELECT ... INTO @Variable prior to the RETURN line.

Step 3: Validate Data Type Compatibility

  • Check that the data type declared in the function header (e.g., RETURNS INT) matches the data type of the expression in the RETURN statement.
  • Use CAST or CONVERT explicitly if there is a mismatch between the variable type and the function’s declared return type.
  • Save and re-deploy the function using CREATE OR ALTER FUNCTION to avoid dropping dependent permissions.

Step 4: Rebuild Dependent Objects

  • Navigate to the Programmability > Stored Procedures folder in SSMS Object Explorer to find any objects calling the fixed function.
  • Execute sp_refreshsqlmodule '<ProcedureName>' on dependent stored procedures to ensure the execution plan cache recognizes the updated scalar return type.
  • Restart the SQL Server Agent service via services.msc on Windows Server 2025 if cached job steps reference the old function schema.

Alternative or Verification Steps

  • Execute the function in isolation using SELECT dbo.FunctionName(@TestParam); to confirm it returns a single value without throwing Error 4133.
  • If the error persists, use sys.dm_exec_describe_first_result_set on the query body to programmatically identify exactly which column or expression is causing the multi-value conflict.