How to fix Error 4982 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4982 – ALTER TABLE SWITCH Partition Mismatch

Why This Error Happens

This error occurs because SQL Server’s partition switching feature requires the source table’s data to be fully validated against the boundary values of the target partition before the metadata switch can occur. Typically, the source table is either missing a CHECK constraint entirely, or the existing constraint logic does not precisely align with the partition function’s boundary range on the target table. Since SQL Server 2025 enforces strict schema validation during switch operations to maintain data integrity, any discrepancy—even a single row outside the defined range—will block the operation entirely.

Step-by-Step Resolution Guide

Step 1: Identify the Partition Boundary Values

  • Open SQL Server Management Studio (SSMS) and connect to your instance.
  • Run a query against sys.partition_range_values and sys.partition_functions to determine the exact boundary values (e.g., LEFT or RIGHT range) for the specific partition number mentioned in the error message.
  • Note the data type and boundary logic (inclusive vs. exclusive) required for the target partition.

Step 2: Audit and Correct the Source Table Constraint

  • Check the existing constraint using sp_helpconstraint 'YourSourceTableName'.
  • Verify if the CHECK constraint matches the boundary values found in Step 1. It must be just as restrictive or more restrictive than the partition range.
  • If the constraint is missing or incorrect, drop the old one and add a new one:
  ALTER TABLE YourSourceTable WITH CHECK 
  ADD CONSTRAINT CK_PartitionRange CHECK (YourColumn >= 'StartValue' AND YourColumn < 'EndValue');

Step 3: Validate Existing Data Against the New Constraint

  • Ensure the constraint is trusted and not just logically present but unenforced.
  • Run the following command to force SQL Server to re-check all existing rows against the constraint:
  ALTER TABLE YourSourceTable WITH CHECK CHECK CONSTRAINT CK_PartitionRange;
  • If this command fails, it will return the specific rows violating the range, allowing you to clean or move that data before retrying the switch.

Step 4: Retry the Partition Switch

  • Navigate back to your original ALTER TABLE ... SWITCH TO ... statement.
  • Execute the command again now that the constraint metadata matches the target partition boundaries.
  • Monitor the “Messages” tab in SSMS for a successful completion status.

Alternative or Verification Steps

  • Verification: Query sys.partitions on the target table immediately after the switch to confirm the rows count has increased in the correct partition number, verifying the metadata update was successful.
  • Alternative: If constraint logic becomes too complex to debug, bypass the check by using ALTER TABLE ... SWITCH ... WITH (TRUNCATE_TARGET = ON) only if you are certain the target partition is intended to be overwritten, though this does not fix underlying data integrity issues for future switches.