Sql Server Identity

How to Reset an Increment Identity’s Starting Value in SQL Server

When working with databases in SQL Server, you may encounter situations where you need to reset an increment identity’s starting value. This can be particularly useful during development or testing phases when you want to ensure that your data starts fresh or cycles through a specific range of values again. In this blog post, we’ll break down the process of how to reset the starting value of an identity column in SQL Server, providing you with a clear and concise guide.

Understanding Identity Columns

Before we dive into the steps for resetting the increment identity value, let’s briefly explain what an identity column is:

  • Identity Column: An identity column is a special column in a SQL Server table that automatically generates a sequential number whenever a new row is added. Typically, this column is defined with the IDENTITY property.

When you CREATE a table with an identity column, you might set it up like this:

CREATE TABLE ExampleTable (
    ID INT IDENTITY(1,1) PRIMARY KEY,
    Name VARCHAR(50)
);

In this example, the first row will have an ID of 1, the second row will have an ID of 2, and so forth, incrementing by 1. However, sometimes you might want to reset this sequence back to a specific number—often 0 or 1—for various reasons, such as when reloading test data.

Resetting the Identity Value

To reset the starting value of an identity column in SQL Server, you can use the DBCC CHECKIDENT command. Here’s a breakdown of how to do it:

Step 1: Identify Your Table

Before making any changes, identify the table whose identity column you want to reset. For this guide, let’s say your table is named TableName.

Step 2: Use the DBCC CHECKIDENT Command

The command syntax to reset the identity value is straightforward:

DBCC CHECKIDENT('TableName', RESEED, 0);
  • DBCC CHECKIDENT: This command checks the current identity value for the specified table and can reset it if needed.
  • ‘TableName’: Replace this with your actual table name.
  • RESEED: This keyword indicates that you want to reset the starting value.
  • 0: This is the new starting value for the identity column. You can change it to whichever value suits your needs, but keep in mind that the first inserted row after this command will take this value and increment from there.

Step 3: Confirm the Reset

To confirm that the identity value has been reset, simply insert a new row into the table and check the ID values:

INSERT INTO TableName (Name) VALUES ('Test Entry');
SELECT * FROM TableName;

You should see that the new entry has an ID of 1 (or 0, depending on the value you set for RESEED) if that was your designated starting point.

Conclusion

Resetting an increment identity’s starting value in SQL Server is a straightforward process using the DBCC CHECKIDENT command. This ability is particularly beneficial during testing or development phases, allowing you to streamline your workflow by ensuring that identifiers are consistent and predictable.

Now you have a solid template for resetting identity columns at your fingertips. Happy coding!