How to fix Error 4955 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: Error 4955 – ALTER TABLE SWITCH Source and Target Table Are Same

Why This Error Happens

Error 4955 occurs when a ALTER TABLE ... SWITCH statement is executed with identical source and target table references, which is structurally invalid because SQL Server requires two distinct table objects (or distinct partitions) to perform a metadata-only data movement. This typically happens due to a scripting error, a copy-paste mistake in dynamically generated SQL, or a misconfigured ETL/partition management job that fails to update table name variables between executions. It can also surface when schema-qualified names resolve to the same underlying object despite appearing different in the script (e.g., same table referenced via a synonym or different case-sensitive alias on a case-insensitive collation).

Step-by-Step Resolution Guide

Step 1: Review the Exact T-SQL Statement Causing the Error

  • Capture the full ALTER TABLE SWITCH command from SQL Server error logs, SSMS query history, or the calling application/job step.
  • Check both the SWITCH source table and the TO target table names, including schema prefixes (e.g., dbo.SalesData_Staging vs dbo.SalesData).
  • Confirm neither name is accidentally duplicated due to a copy-paste error in a stored procedure or dynamic SQL block.

Step 2: Inspect Dynamic SQL and Variable Assignments

  • If the switch is generated programmatically (common in partition management scripts or SSIS packages), open the source code and verify the variables holding source/target table names are populated independently.
  • Look for logic errors such as @TargetTable = @SourceTable or a loop that fails to increment/reassign the target partition table on each iteration.
  • Add temporary PRINT or SELECT statements before the ALTER TABLE SWITCH execution to output both variable values for validation.

Step 3: Verify Table Identity and Synonyms

  • Run SELECT OBJECT_ID('SchemaName.TableName') against both the source and target table names to confirm they resolve to different object IDs.
  • Check for synonyms using sys.synonyms that might silently point both references to the same base table.
  • If using a case-insensitive collation, confirm the two table names aren’t simply case variations of the same physical object.

Step 4: Correct the Script and Re-run in a Test Environment

  • Update the source or target reference so they point to genuinely separate tables/partitions.
  • Test the corrected ALTER TABLE SWITCH statement in a non-production database first, especially if this is part of an automated partition rollover job on Windows Server 2025.
  • Deploy the fix to the production job/script only after confirming successful execution.

Alternative or Verification Steps

  • Re-execute the corrected ALTER TABLE SWITCH statement and confirm it completes without Error 4955, then validate row counts moved from source to target partition using sys.partitions.
  • If the error persists in an automated job, enable verbose logging or a TRY...CATCH block in the stored procedure to capture the exact table names being passed at runtime for deeper debugging.