How to fix Error 13079 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 13079 — Variable Assignment Failure

Why This Error Happens

Error 13079 in Microsoft SQL Server 2025 typically occurs when a Transact-SQL batch or stored procedure attempts to assign a value to a variable using an incompatible data type, an out-of-scope reference, or a malformed SELECT/SET assignment statement. This is often triggered by schema changes (such as a column being dropped, renamed, or having its data type altered) that were not reflected in dependent scripts or precompiled execution plans. In some cases, corrupted plan cache entries on Windows Server 2025 or Windows 11 instances can also cause the engine to misread variable metadata during execution.

Step-by-Step Resolution Guide

Step 1: Validate the Variable Declaration and Data Type

  • Open the offending stored procedure or script in SQL Server Management Studio (SSMS).
  • Confirm the variable is declared with a compatible type, e.g., DECLARE @OrderTotal DECIMAL(10,2);
  • Cross-check the source column’s data type using sp_help 'TableName'; to ensure no mismatch exists after a recent schema update.

Step 2: Clear and Rebuild the Procedure Cache

  • Run the following command to remove stale execution plans that may reference outdated variable metadata:
  DBCC FREEPROCCACHE;
  • Recompile the specific stored procedure to force SQL Server to regenerate its execution plan:
  EXEC sp_recompile 'YourStoredProcedureName';

Step 3: Check for Scope and Batch Separation Issues

  • Ensure the variable is not referenced outside its declared batch (i.e., after a GO statement), as this will cause SQL Server to lose scope.
  • Verify there are no nested BEGIN...END blocks accidentally isolating the DECLARE statement from the assignment line.

Step 4: Update SQL Server Cumulative Updates

  • On Windows Server 2025 or Windows 11, open SQL Server Configuration Manager and confirm the current build version via:
  SELECT @@VERSION;
  • Navigate to the Microsoft Update Catalog and install the latest Cumulative Update (CU) for SQL Server 2025, as early builds have known metadata-reading bugs tied to Error 13079.

Step 5: Rebuild Corrupted Statistics or Indexes

  • If the variable is populated via a SELECT from a table with corrupted statistics, run:
  DBCC CHECKDB('YourDatabaseName') WITH NO_INFOMSGS;
  • Update statistics manually: UPDATE STATISTICS YourTableName;

Alternative or Verification Steps

  • To verify the fix, re-execute the stored procedure in a test environment with SET STATISTICS IO, TIME ON; enabled and confirm no errors are thrown in the Messages tab.
  • If the error persists, isolate the issue by rewriting the assignment using a SELECT TOP 1 @Variable = Column FROM Table pattern instead of implicit SET assignments, as this often bypasses edge-case parser bugs in early SQL Server 2025 builds.