One of the key features of SQL Server is the ability to automatically generate unique values for a column using the identity property. This is particularly useful when you need to create a primary key or a unique identifier for each row in a table. In this blog post, we will explore different ways to identify and work with identity columns in SQL Server.

Finding Identity Columns

There are several methods to find identity columns in a database. One approach is to query the system tables directly. For example, the following query retrieves a list of all column names with their corresponding table names:

SELECT SCHEMA_NAME(so.schema_id) AS SchemaName, so.name AS TableName, sc.name AS ColumnName
FROM sys.objects so
INNER JOIN sys.columns sc ON so.OBJECT_ID = sc.OBJECT_ID
WHERE sc.is_identity = 1;

This query joins the sys.objects and sys.columns system tables and filters the results to only include columns with the is_identity property set to 1.

Another way to find identity columns is by using the $IDENTITY function. This function returns the identity value for the most recently inserted row in a table. Here is an example:

DECLARE @t TABLE (
    GuidCol UNIQUEIDENTIFIER DEFAULT newsequentialid() ROWGUIDCOL,
    IDENTITYCL INT IDENTITY(1, 1),
    data VARCHAR(60)
)

INSERT INTO @t (data) SELECT 'test'
INSERT INTO @t (data) SELECT 'test1'

SELECT $rowguid, $IDENTITY FROM @t;

In this example, we create a table with an identity column and insert two rows. The $IDENTITY function is then used to retrieve the identity values for the inserted rows.

Working with Identity Columns

Once you have identified the identity columns in your database, you can leverage their unique values for various purposes. For example, you can use them as primary keys to ensure data integrity and efficient data retrieval. Additionally, you can use the identity values to track the order of insertion or to generate sequential numbers for specific operations.

It is important to note that while identity columns provide a convenient way to generate unique values, they have certain limitations. For instance, if you need to insert specific values into an identity column, you must explicitly set the IDENTITY_INSERT property to ON for that table.

Furthermore, if you want to reset the identity value for a table, you can use the DBCC CHECKIDENT command. This command allows you to reseed the identity column to a specific value.

Conclusion

Identity columns are a powerful feature in SQL Server that simplify the generation of unique values for columns. By understanding how to identify and work with identity columns, you can effectively utilize them in your database design and data manipulation tasks. Whether you need to create primary keys, track insertion order, or generate sequential numbers, identity columns provide a reliable solution.

Do you have any alternate methods or tips for working with identity columns in SQL Server? Share your thoughts and experiences in the comments below!