How to fix Error 322 on Windows Server 2025 / Windows 11

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Why This Error Happens

Error 322 occurs when SQL Server’s query optimizer encounters a variable in the OPTIMIZE FOR clause that is either undeclared, out of scope, or mismatched in data type with the variable used elsewhere in the query. This typically happens due to a typo in the variable name, a variable declared inside a different batch or dynamic SQL context, or when the variable is scoped to a stored procedure parameter that isn’t visible to the query hint parser. It can also surface after a SQL Server 2025 upgrade if legacy T-SQL scripts use deprecated variable-binding syntax that the new query optimizer no longer tolerates silently.

Step-by-Step Resolution Guide

Step 1: Verify Variable Declaration and Scope

  • Open the query or stored procedure in SQL Server Management Studio (SSMS) and locate the OPTIMIZE FOR (@variable = value) clause.
  • Confirm the variable is declared with DECLARE @variable in the same batch, above the query, and not inside a nested EXEC or dynamic SQL string.
  • Check for typos — variable names are case-sensitive in some collations and must match exactly, including the @ prefix.

Step 2: Check Data Type Compatibility

  • Run sp_help or inspect the DECLARE statement to confirm the variable’s data type matches the column or parameter it’s being compared against.
  • If the variable was declared as NVARCHAR but the OPTIMIZE FOR value is passed as VARCHAR or an incompatible literal, correct the cast:
  • DECLARE @var NVARCHAR(50) = N'SampleValue';
  • Rewrite the clause explicitly: OPTION (OPTIMIZE FOR (@var = N'SampleValue')).

Step 3: Review Compatibility Level and Deprecated Hints

  • Open SSMS, right-click the database → Properties → Options, and check the Compatibility Level field (should be 170 for SQL Server 2025).
  • If using OPTIMIZE FOR UNKNOWN, ensure this syntax is still valid in your compatibility mode; older hint patterns may need updating.
  • Run the query in isolation using sqlcmd -S <ServerName> -Q "YourQueryHere" from an elevated PowerShell/Command Prompt on Windows Server 2025 to isolate parser-level issues outside SSMS caching.

Step 4: Clear Cached Execution Plans

  • Execute DBCC FREEPROCCACHE; to remove any stale cached plans that may reference an old variable definition.
  • Restart the SQL Server service via Services.msc (Windows Server 2025/Windows 11) if the error persists after clearing cache: net stop MSSQLSERVER && net start MSSQLSERVER.

Alternative or Verification Steps

  • Re-run the query with SET SHOWPLAN_TEXT ON; to confirm the optimizer accepts the OPTIMIZE FOR clause without throwing Error 322.
  • If the issue persists, replace OPTIMIZE FOR (@variable = value) with OPTIMIZE FOR UNKNOWN as a temporary workaround while auditing the procedure for the exact variable mismatch.