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In general, if your application having an audit trial feature (to records any add, edit & delete activity performed by any end user in each table), it would be value addition to your application or it may be the best selling point of your application. However, when it comes to the development of this feature, it really become a nightmare. The reason for being problematic is that you need to integrate this feature everywhere in your application. In addition, you need to develop so many audit tables, stored procedures & triggers in order to achieve it. Sometimes the development and testing of this feature takes long time.
In SQL Server 2008, this problem has been solved by shipping a new feature namely Change data capture. It is one of the biggest and remarkable features in SQL Server 2008. In fact, it records and maintains all the changes in any table (if enabled) with very minimal amount of efforts and the good news is that the developers do not need to write even single a line of code to capture all these changes :).

In this article, I will demonstrate how to enable Change Data Capture (CDC) for any database and tables step by step.

Step 1 :
Before enabling CDC for any database, you must check whether it is already enabled or not. Given below is the script that shows all the databases along with its CDC enabled status.

--This script is compatible with SQL Server 2008 and above.
USE master
GO
SELECT
database_id,
name,
is_cdc_enabled
FROM sys.databases
GO
--OUTPUT

Step 2 :
In step 1, as you observed that all the is_cdc_enabled columns of sys.database (system view) is 0. It means that none of the databases has been enabled for CDC.
Lets enable CDC for AdventureWorks2012 database in this step. Given below is the script.

--This script is compatible with SQL Server 2008 and above.
--DONOT forget to change the database name below.
USE AdventureWorks2012
GO
EXEC sys.sp_cdc_enable_db
GO

Step 3 :
Once you enabled the CDC, you need to repeat step 1, in order to check whether CDC has been enabled for AdventureWorks2012 database or NOT.
Given below is the same script but the output would be different.

--This script is compatible with SQL Server 2008 and above.
USE master
GO
SELECT
database_id,
name,
is_cdc_enabled
FROM sys.databases
GO
--OUTPUT

As you can see that is_cdc_enabled column value is 1 for AdventureWorks2012 database and it is a confirmation that CDC is enabled for AdventureWorks2012 database.

Step 4 :
Once you enable the CDC in the database lets enable the CDC in a table in order to capture the changes in that particular table.
But hang on a minute, before activating this feature on any table, you must check whether it is already enabled for that particular table or not. Given below is the script that will list down all the tables available in that particular database along with the CDC status.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT
object_id,
SCHEMA_NAME(Schema_id) As [Schema Name],
name As [Table Name],
is_tracked_by_cdc
FROM sys.tables
GO
--OUTPUT

Step 5 :
In step 5, as you noticed that all the is_cdc_enabled columns of sys.database (system view) is 0. It means that none of the databases has been enabled for CDC.
Lets enable CDC for table namely HumanResources.Department in AdventureWorks2012 database in this step. Given below is the script.

--This script is compatible with SQL Server 2008 and above.
--DONOT forget to change the database name below.
USE AdventureWorks2012
GO
EXEC sys.sp_cdc_enable_table
@source_schema = N'HumanResources',
@source_name = N'Department',
@role_name = NULL
GO

As you can see above one of the parameters @role_name is NULL. I deliberately made it NULL, so all the users belonging to any role can view the changes in that particular table. However, you can pass any role to restrict the access from other users & roles accordingly.

Step 6 :
In this step, we need to check again if CDC has been enabled for that particular table or not. In order to do it, we need to repeat step 3 and this time the result set would be different. Given below is the same script as Step 4.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT
object_id,
SCHEMA_NAME(Schema_id) As [Schema Name],
name As [Table Name],
is_tracked_by_cdc
FROM sys.tables
GO
--OUTPUT

Step 7 :
Now, we assured that CDC has been enabled for that particular table, it means that CDC has created an audit table for that particular table (Same way we used to manually create in earlier version of SQL Server to record audit for any table). But where is that particular audit table ? You will find that particular table in CDC schema as shown below.

In my upcoming article, I will write how to manipulate the CDC feature and how we can view those changes in order to really enjoy the audit trial feature with zero customization.

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