How to fix Error 5367 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 5367

Why This Error Happens

Error 5367 occurs when a T-SQL query attempts to redefine a named window (using the WINDOW clause or inline OVER() specification) that has already been declared earlier in the same query batch. This typically results from copy-paste errors in complex analytical queries, duplicate alias names across CTEs or subqueries, or a corrupted/outdated query plan cache retaining a stale window definition. In SQL Server 2025, this can also surface when application code dynamically generates window functions and inadvertently reuses a window name across unioned or nested query blocks.

Step-by-Step Resolution Guide

Step 1: Identify the Duplicate Window Definition

  • Open the query in SQL Server Management Studio (SSMS) 21 and locate all instances of the WINDOW keyword.
  • Search for repeated alias names (e.g., WINDOW w1 AS (...)) appearing more than once in the same scope.
  • Use Ctrl+F with “Find All” to scan the full batch, including nested subqueries and CTEs.

Step 2: Rename or Consolidate Conflicting Window Specifications

  • If two windows are functionally identical, remove the duplicate and reference the single named window in all OVER(w1) clauses.
  • If the windows are meant to be different, rename the second occurrence (e.g., w2) and update all corresponding OVER() references.
  • Ensure each WINDOW clause is scoped correctly to its own SELECT statement rather than leaking across UNIONed blocks.

Step 3: Clear the Plan Cache and Recompile

  • Run DBCC FREEPROCCACHE in a non-production environment to eliminate stale cached execution plans tied to the old window definition.
  • Alternatively, use sp_recompile 'YourProcedureName' for a targeted recompilation of the affected stored procedure.
  • Re-execute the corrected query to confirm the batch compiles without Error 5367.

Step 4: Audit Application-Generated SQL

  • If the query is built dynamically (e.g., via an ORM or string concatenation in C#/.NET), inspect the code path that appends WINDOW clauses.
  • Add validation logic to prevent duplicate alias names from being generated when loops or recursive functions construct the query.

Alternative or Verification Steps

  • Execute the revised query directly in SSMS or Azure Data Studio and confirm it returns results without raising Error 5367.
  • If the error persists, use SET SHOWPLAN_XML ON to inspect the query execution plan for any residual references to the conflicting window name before re-deploying the fix.