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Summary: Understanding the process and restrictions of updating an identity column in SQL Server.
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How to Update an Identity Column in SQL Server

When working with SQL Server, the concept of identity columns is crucial for automatically generating unique values for new rows, typically used for primary keys. However, questions often arise about whether and how these identity columns can be updated. This post aims to provide comprehensive insights on this topic.

Can We Update the Identity Column in SQL Server?

By default, identity columns in SQL Server are designed to generate sequential unique numbers, and such columns are inherently protected against direct updates. The SQL Server syntax does not support direct updates to an identity column because its primary purpose is to maintain data integrity and consistency.

Common Scenarios Needing Identity Column Updates

Even though direct updates are not allowed, there might be scenarios requiring modifications to identity values:

Data Migration: Migrating data from an old database that uses different identity values.

Data Correction: Correcting mistaken entries.

Renumbering Rows: Reorganizing identity values for sequence changes.

Approaches to "Update" an Identity Column

Although direct updates are not possible, there are alternative methods to achieve similar objectives.

Using SET IDENTITY_INSERT

The SET IDENTITY_INSERT command allows explicit values to be inserted into the identity column for a table for a particular session.

Insert Desired Values:

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Reinserting Rows with Updated Identities:

Create a new table with the same structure but without an identity column.

Insert records from the original table, modifying identity values as necessary.

Drop the original table and rename the new table.

Example: Transfer Rows to a New Table

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Using Temporary Tables

Another strategy is to use temporary tables for interim storage during transformations.

Create a temporary table:

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Populate temporary table and switch data:

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Conclusion

Direct updates to identity columns in SQL Server are not permitted to preserve data consistency and integrity. However, alternative methods such as utilizing SET IDENTITY_INSERT or leveraging temporary tables can fulfill the need for updating identity column values. Understanding these approaches allows you to work within the limitations while maintaining the structured operation of your SQL Server databases.

By following these guidelines, you can effectively handle scenarios where identity values need to be manipulated without jeopardizing the database integrity.