SQL Server Reseed Identity: A Comprehensive Guide for Dev

Hello Dev! Are you struggling with resetting the identity value in your SQL Server database? If you are, this article is for you. In this comprehensive guide, we will cover everything you need to know about reseeding identity in SQL Server. By the end of this article, you will be able to reset the identity value of a table in SQL Server with ease. So, let’s get started!

Introduction to Identity in SQL Server

Before we dive into reseeding identity, let’s first understand what identity is in SQL Server. Identity is a feature in SQL Server that allows you to automatically generate unique values for a column. This is especially useful when you have a table that requires a unique identifier for each row. The identity column is often used as the primary key for the table.

When you create a table in SQL Server, you can specify a column as an identity column by using the IDENTITY keyword. For example, the following SQL code creates a table with an identity column:

CREATE TABLE Employees
(
EmployeeID INT IDENTITY(1,1) PRIMARY KEY,
FirstName VARCHAR(50),
LastName VARCHAR(50),
);

In this code, the IDENTITY keyword specifies that the EmployeeID column is an identity column. The two values in the parentheses (1,1) specify the starting value and increment for the identity values.

Understanding Reseeding Identity in SQL Server

Reseeding identity is the process of resetting the identity value of a table. This process is useful when you want to start the identity values from a specific value, rather than the default starting value. For example, if you have a table that already has data, but you want to start the identity values from a specific number, you can use the reseed identity feature.

To reseed identity, you need to use the DBCC CHECKIDENT command. This command allows you to check and modify the current identity value of a table. The syntax for the command is as follows:

DBCC CHECKIDENT (table_name [, { NORESEED | { RESEED [, new_reseed_value ] } } ] )

The table_name parameter specifies the name of the table whose identity value you want to reseed. The NORESEED option tells the command not to change the current identity value. The RESEED option tells the command to reset the identity value to the specified value, which is passed as the new_reseed_value parameter.

Reseeding Identity in SQL Server: Step-by-Step Guide

Now that you understand what reseeding identity is in SQL Server, let’s take a look at how to perform reseeding identity step-by-step:

Step 1: Connect to your SQL Server instance

The first step is to connect to your SQL Server instance using SQL Server Management Studio or any other database management tool. Once you have connected to your SQL Server instance, open a new query window.

Step 2: Identify the table whose identity value you want to reseed

The next step is to identify the table whose identity value you want to reseed. You can do this by using the following SQL command:

SELECT name FROM sys.tables WHERE OBJECTPROPERTY(OBJECT_ID,'TableHasIdentity') = 1

This command will list all the tables in the current database that have an identity column. Identify the table whose identity value you want to reseed.

Step 3: Check the current identity value of the table

The next step is to check the current identity value of the table. You can do this by using the following SQL command:

DBCC CHECKIDENT('table_name')

This command will display the current identity value of the table. Note down this value as you will need it later.

Step 4: Reseed the identity value of the table

Now that you have identified the table and checked its current identity value, you can reset the identity value by using the following SQL command:

DBCC CHECKIDENT('table_name', RESEED, new_reseed_value)

Replace table_name with the name of the table you want to reseed and new_reseed_value with the value you want to start the identity values from. For example, if you want to start the identity values from 100, you would use the following command:

DBCC CHECKIDENT('Employees', RESEED, 100)

Execute this command to reset the identity value of the table.

Step 5: Verify the new identity value

The final step is to verify that the identity value has been reset to the desired value. You can do this by using the following SQL command:

DBCC CHECKIDENT('table_name')

This command will display the current identity value of the table. Make sure that the identity value has been reset to the desired value.

FAQs about SQL Server Reseed Identity

Q1: Can I change the increment value of an identity column?

A1: Yes, you can change the increment value of an identity column. To do this, you need to drop and recreate the identity column with the new increment value.

Q2: Can I reseed the identity value of a table with data?

A2: Yes, you can reseed the identity value of a table with data. However, you need to make sure that the new identity values do not conflict with existing values.

Q3: What happens if I reseed the identity value to a value that already exists in the table?

A3: If you reseed the identity value to a value that already exists in the table, you will get a duplicate key error when you try to insert a new row with an identity value equal to the reseeded value.

Q4: Can I reseed the identity value of a table to a negative value?

A4: No, you cannot reseed the identity value of a table to a negative value.

Q5: Can I reseed the identity value of a table back to its original value?

A5: Yes, you can reseed the identity value of a table back to its original value. To do this, you need to check the current identity value of the table and then use that value as the new_reseed_value parameter of the DBCC CHECKIDENT command.

Conclusion

Reseeding identity in SQL Server is an important feature that allows you to reset the identity value of a table. This process is useful when you want to start the identity values from a specific value. In this article, we covered everything you need to know about reseeding identity in SQL Server. We hope that this guide has helped you to understand how to reseed identity and how to use the DBCC CHECKIDENT command. If you have any further questions, feel free to leave a comment below.