How to Efficiently Remove Identity from a SQL Server Table Column Using T-SQL?

Removing the Identity Property from a SQL Server Table Column

Dealing with large SQL Server tables (exceeding 5GB) requires careful consideration when modifying column properties. Directly removing the identity property through SQL Server Management Studio (SSMS) can lead to timeouts. This guide provides a T-SQL-based solution.

T-SQL Approach:

While you can't directly remove the identity attribute once assigned, T-SQL offers a workaround.

Method 1: Dropping the Entire Column:

If the column's data is no longer needed, the simplest solution is to drop it:

ALTER TABLE yourTable
DROP COLUMN yourColumn;

Method 2: Preserving Data While Removing Identity:

To retain the column's data while removing the identity property, follow these steps:

1. Create a New Column: Add a new column to hold the existing data.
2. Transfer Data: Copy the data from the original identity column to the new column.
3. Drop the Original Column: Remove the original identity column.
4. Rename the New Column: Rename the new column to match the original column's name.

Example using a Customers table with an CustomerID identity column:

ALTER TABLE Customers
ADD CustomerID_New INT NOT NULL;

UPDATE Customers
SET CustomerID_New = CustomerID;

ALTER TABLE Customers
DROP COLUMN CustomerID;

EXEC sp_rename 'Customers.CustomerID_New', 'CustomerID', 'COLUMN';

Important Considerations:

This method, while effective, involves multiple steps and can be time-consuming, particularly for large tables. Consider the impact on performance and plan accordingly. The sp_rename command explicitly specifies 'COLUMN' to ensure the correct renaming operation.

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