Should You Reset the Identity Seed After Deleting Records in SQL Server?

2024-06-30

Deleting records from a table with an identity column doesn't reset that counter. The gaps created by deletions are simply skipped. This is because the identity column values are used to link data between tables. Resetting them would break these connections.

There are two main things to know about this:

  1. Identity Column and Deleted Records:
  • Deleting records doesn't affect the identity column's counter. It keeps incrementing from where it left off, leaving gaps in the numbering.
  1. Why Not Reset the Counter?
  • Identity column values are often used as foreign keys to link data in other tables. Resetting the counter would invalidate these links, causing data integrity issues in your database.

Alternatives to Resetting the Counter:

  • Leave the Gaps: This is the most common approach. The gaps don't affect how the data works, they just create a non-sequential numbering.
  • Use a Different Column as Primary Key: If you don't need the automatic numbering and gaps bother you, consider using another unique column (like a combination of existing columns) as the primary key.

If Absolutely Necessary: Resetting with Caution (Risky):

There's a risky way to reset the counter, but it's generally not recommended. It involves:

  1. Backing up your table.
  2. Deleting all data from the table.
  3. Using a command called DBCC CHECKIDENT to reset the counter to a new value.
  4. Re-inserting the backed-up data.

This approach is risky because if something goes wrong during the process, you could lose your data.

In Summary:

  • Deleting records doesn't reset the identity column counter.
  • Resetting the counter is risky and usually not needed.
  • Consider alternative approaches like leaving gaps or using a different primary key.



Truncate Table and Reset Seed:

This approach uses TRUNCATE TABLE which removes all data but keeps the table structure. Then, it resets the identity seed using DBCC CHECKIDENT.

-- Truncate the table (removes all data)
TRUNCATE TABLE MyTable;

-- Reset the identity seed to 0
DBCC CHECKIDENT ('MyTable', RESEED, 0);

-- Optionally, reset again to set the seed to the highest existing value (safer)
DBCC CHECKIDENT ('MyTable', RESEED);

Delete All and Reset Seed (Less Safe):

This approach deletes all data with DELETE and then resets the seed. This is less safe because DELETE allows for potential rollback compared to TRUNCATE.

-- Delete all data from the table
DELETE FROM MyTable;

-- Reset the identity seed to 0
DBCC CHECKIDENT ('MyTable', RESEED, 0);

-- Optionally, reset again to set the seed to the highest existing value (safer)
DBCC CHECKIDENT ('MyTable', RESEED);

Important Notes:

  • These examples are for demonstration purposes only. Resetting the identity seed should be done with caution and only if there's a strong reason.
  • Always back up your table before making any changes.
  • Consider the impact on foreign keys and data integrity before resetting.



  1. Leave the Gaps:

This is the simplest and most common approach. Deleted records leave gaps in the identity column numbering. These gaps don't affect how the data functions within the database. The data itself will still be linked correctly using the existing identity values.

  1. Use a Different Column as Primary Key:

If you don't need the automatic numbering feature of the identity column and the gaps bother you, consider using a different, unique column (or a combination of existing columns) as the primary key for the table. This eliminates the need for an identity column altogether.

Here are some additional options depending on your specific needs:

  1. Calculated Column for Display Purposes:

If you need a sequential numbering for display purposes only (e.g., for user interfaces), you can create a calculated column that generates a running number based on the existing identity column. This calculated column won't affect the actual data storage or relationships.

  1. Separate Sequence Table (For Complex Scenarios):

In very specific scenarios, you might consider using a separate table to generate a sequence of numbers. This table would have its own identity column and logic for generating unique numbers. You can then link this sequence table to your main table to assign these separate sequence numbers to your data.

Choosing the Right Approach:

The best approach depends on your specific needs and the structure of your database.

  • If you don't need continuous numbering and gaps aren't an issue, leaving the gaps is the simplest solution.
  • If you need a different primary key altogether, consider using a unique existing column or a combination.
  • For display purposes only, a calculated column based on the identity can work.
  • A separate sequence table is a complex option best suited for very specific scenarios.

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