Reset Identity in SQL Server

Greetings, Dev! If you’re here, you’re probably dealing with a common issue in SQL Server – resetting the identity column. Don’t worry, this is a common problem and can be easily fixed. In this article, we’ll guide you through the process of resetting an identity column in SQL Server.

Understanding Identity Column in SQL Server

Before we start, it’s important to understand what an identity column is in SQL Server. An identity column is a column that generates a unique value for each row in a table. It’s usually used as a primary key and is set to increment automatically with every new row inserted into the table.

However, sometimes we may need to reset the identity column, either to renumber the rows or to reuse the numbers of deleted rows. Let’s look at the different scenarios where we may need to reset the identity column in SQL Server.

Scenario 1: Renumbering Rows

One scenario where we may need to reset the identity column is when we want to renumber the rows in a table. This may be necessary when we’re dealing with data that’s imported from another system or when we want to change the order of the rows.

To reset the identity column in this scenario, we’ll need to create a new column, update it with the desired values, and then drop the old identity column. Let’s see how to do this in SQL Server.

Scenario 2: Reusing Numbers of Deleted Rows

Another scenario where we may need to reset the identity column is when we want to reuse the numbers of deleted rows. When we delete a row from a table, the identity column continues to increment, and the next row inserted will have a new value.

If we want to reuse the numbers of deleted rows, we’ll need to reset the identity column manually. This can be done by truncating the table or by using DBCC CHECKIDENT command. Let’s see how to do this in SQL Server.

How to Reset Identity Column in SQL Server

Now that we know the different scenarios where we may need to reset the identity column, let’s see how to do it in SQL Server.

Step 1: Create a New Table

The first step in resetting the identity column is to create a new table with the same structure as the original table. We’ll use this new table to copy the data from the old table.

Here’s the syntax to create a new table in SQL Server:

CREATE TABLE new_table_name (

column1 datatype,

column2 datatype,

…

);

Replace “new_table_name” with the desired name of the new table and “column1”, “column2”, etc. with the column names and data types of the original table.

Step 2: Copy Data from Old Table to New Table

Once we have the new table, we can copy the data from the old table to the new table using the INSERT INTO statement. Here’s the syntax:

INSERT INTO new_table_name (column1, column2, …)

SELECT column1, column2, …

FROM old_table_name;

Replace “new_table_name” with the name of the new table, “column1”, “column2”, etc. with the column names of the original table, and “old_table_name” with the name of the original table.

Step 3: Drop the Old Table

Once the data is copied to the new table, we can drop the old table using the DROP TABLE statement. Here’s the syntax:

DROP TABLE old_table_name;

Replace “old_table_name” with the name of the original table.

Step 4: Rename the New Table to Old Table Name

After we’ve dropped the old table, we can rename the new table to the old table name using the sp_rename system stored procedure. Here’s the syntax:

sp_rename ‘new_table_name’, ‘old_table_name’;

Replace “new_table_name” with the name of the new table and “old_table_name” with the name of the original table.

Step 5: Reset the Identity Column

If we want to reuse the numbers of deleted rows, we can reset the identity column by using the DBCC CHECKIDENT command. Here’s the syntax:

DBCC CHECKIDENT (‘table_name’, RESEED, new_reseed_value);

Replace “table_name” with the name of the table and “new_reseed_value” with the desired starting value for the identity column.

If we want to renumber the rows in the table, we’ll need to create a new identity column and drop the old identity column. Here’s the syntax:

ALTER TABLE table_name ADD new_identity_column int IDENTITY (new_start_value, new_increment_value);

UPDATE table_name SET new_identity_column = old_identity_column;

ALTER TABLE table_name DROP COLUMN old_identity_column;

EXEC sp_rename ‘table_name.new_identity_column’, ‘old_identity_column’, ‘COLUMN’;

Replace “table_name” with the name of the table, “new_identity_column” with the desired name of the new identity column, “old_identity_column” with the name of the old identity column, “new_start_value” with the desired starting value for the identity column, and “new_increment_value” with the desired increment value for the identity column.

FAQ

Q1. Can we reset the identity column for a specific row in a table?

No, we cannot reset the identity column for a specific row in a table. The identity column is designed to generate a unique value for each row in the table, and changing it for a specific row would violate this rule.

Q2. Can we change the increment value of an identity column?

Yes, we can change the increment value of an identity column using the ALTER TABLE statement. Here’s the syntax:

ALTER TABLE table_name ALTER COLUMN identity_column_name int IDENTITY (new_start_value, new_increment_value);

Replace “table_name” with the name of the table, “identity_column_name” with the name of the identity column, “new_start_value” with the desired starting value for the identity column, and “new_increment_value” with the desired increment value for the identity column.

Q3. Can we set the identity column to a specific value when inserting data into a table?

No, we cannot set the identity column to a specific value when inserting data into a table. The identity column is designed to generate a unique value for each row in the table, and changing it for a specific row would violate this rule.

Conclusion

Resetting the identity column in SQL Server may seem like a daunting task, but with the right steps, it can be easily accomplished. Whether you need to renumber the rows or reuse the numbers of deleted rows, we’ve shown you how to do it in SQL Server. If you have any other questions or concerns, feel free to leave a comment below. Happy resetting, Dev!