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How to reset identity seed after deleting records in SQL Server?

In SQL Server, when you delete rows from a table with an identity column, the identity seed (auto-increment value) does not automatically reset. If you need to “restart” the identity value (for example, to remove gaps in the sequence), you can use DBCC CHECKIDENT.

1. Using DBCC CHECKIDENT

DBCC CHECKIDENT allows you to reset the current identity value for a specific table.

DBCC CHECKIDENT ('YourTableName', RESEED, NewSeedValue);
  • YourTableName: Fully qualified table name (including schema if necessary, e.g., dbo.Employees).
  • RESEED: The command instructing SQL Server to change the current identity value.
  • NewSeedValue: The next identity number you want the table to use. If you want the next row inserted to start at 1, set this to 0 (SQL Server then increments it on the next insert to 1).

2. Example: Reset to Start at 1 Again

Assume you have a table dbo.Employees with a primary key identity column named EmployeeID. If you’ve truncated or deleted all rows and want the identity to restart at 1:

DBCC CHECKIDENT ('dbo.Employees', RESEED, 0);

On the next insert, the EmployeeID will be set to 1.

3. Important Considerations

  1. Data Integrity: If other tables reference the identity column, reseeding might cause confusion or invalid references.
  2. Concurrency: In a production environment with concurrent inserts, ensure no other sessions are trying to insert rows at the same time.
  3. TRUNCATE vs. DELETE: Truncating a table automatically resets the identity seed to the original start value, while deleting records does not.

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  1. Grokking SQL for Tech Interviews – Dive into query optimization, indexing, and tackling complex SQL problems commonly asked in interviews.
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Conclusion

Resetting an identity seed after deleting rows can keep your primary key values tidy for reporting or aesthetic reasons. Use DBCC CHECKIDENT to manually reseed the table and remember to consider data integrity, referencing foreign keys, and concurrency issues before doing so in a production environment.

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