In this blog post, we will explore the concept of Identity Fields in SQL Server and how they can be used to automatically generate unique values for a specific column in a table.

What are Identity Fields?

An Identity Field, also known as an Identity Column, is a column in a table that is automatically populated by SQL Server with a unique value for each new row inserted into the table. The values in an Identity Field are typically used as primary keys or unique identifiers for the records in the table.

When a new row is inserted into a table with an Identity Field, SQL Server automatically generates a new value for the Identity Field based on the specified increment and seed values. The increment value determines how much the Identity Field should increase for each new row, while the seed value determines the starting value for the Identity Field.

Using Identity Fields

Let’s consider an example where we have a table called “CurrentProducts” with an Identity Field called “ProductID”. The “ProductID” column is set as an Identity Field, which means that SQL Server will automatically generate a unique value for each new row inserted into the table.

For example, if we insert a new row into the “CurrentProducts” table without specifying a value for the “ProductID” column, SQL Server will automatically generate the next available value for the Identity Field:

INSERT INTO CurrentProducts (ProductName, RetailPrice, OriginationDate, ToBeDeleted, Category) 
VALUES ('Yoga Mtn Getaway 5 Days', 875.00, '9/1/2009', 0, 'Medium-Stay')

After executing this query, SQL Server will generate a new value for the “ProductID” column and insert the row into the table.

Overriding Identity Fields

Sometimes, we may want to manually specify a value for an Identity Field instead of relying on SQL Server to generate it automatically. This can be useful in scenarios where we want to maintain a specific sequence of values or avoid gaps in the Identity Field values.

To override the automatic generation of Identity Field values, we need to temporarily enable the IDENTITY_INSERT property for the table. This property allows us to manually insert values into the Identity Field.

Here’s an example of how to override the Identity Field and manually insert a value:

SET IDENTITY_INSERT CurrentProducts ON

INSERT INTO CurrentProducts (ProductID, ProductName, RetailPrice, OriginationDate, ToBeDeleted, Category) 
VALUES (481, 'Yoga Mtn Getaway 5 Days', 875.00, '9/1/2009', 0, 'Medium-Stay')

SET IDENTITY_INSERT CurrentProducts OFF

In this example, we first enable the IDENTITY_INSERT property for the “CurrentProducts” table. Then, we manually insert a row into the table with a specific value for the “ProductID” column. Finally, we disable the IDENTITY_INSERT property to allow SQL Server to resume automatic generation of Identity Field values.

Conclusion

Identity Fields are a powerful feature in SQL Server that allow for the automatic generation of unique values for a specific column in a table. They can greatly simplify the management of primary keys and unique identifiers in a database. However, there may be scenarios where we need to override the automatic generation of Identity Field values and manually insert specific values. By understanding how to use and override Identity Fields, we can have more control over the values in our tables.