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Every database administrator has been faced with the need to track changes to data at one point or another. Thanks to Microsoft, we have a powerful tool at our disposal to make this usually complicated task easier called the SQL Server Change Data Capture feature. In this blog post, we’ll dive into what it is, how to set it up, and show you some useful SQL code examples.
What is SQL Server Change Data Capture?
Change Data Capture (CDC) is a feature introduced in SQL Server 2008. It is designed to capture changes (insert, update, delete operations) made to SQL Server Tables. CDC uses the SQL Server’s transaction log to track these changes and stores the information in change tables, making the task of data change tracking easier and more efficient.
Setting up CDC
To enable CDC, you simply use the sys.sp_cdc_enable_db or the sys.sp_cdc_enable_table stored procedures in your SQL Server. Keep in mind that you would need permissions to perform this action. Here’s how it works:
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-- Enable CDC on the database EXEC sys.sp_cdc_enable_db GO -- Enable CDC on a specific table EXEC s<a href="mailto:ys.sp_cdc_enable_table @source_schema" >ys.sp_cdc_enable_table @source_schema</a> = 'dbo', @source_name = 'Customers', @role_name = 'CDCRole' GO |
This code will enable CDC on the ‘Customers’ table and create a role named ‘CDCRole’. By specifying role_name parameter, we are permitting role members to access change data.
Tracking Changes
Once CDC is enabled, SQL Server automatically tracks changes to the specific table. These changes are stored in specially created change tables that are easily readable and consumable for further processing. Let’s say we have made changes to the ‘Customers’ table, to view these changes, we use the function like below:
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SELECT * FROM cdc.fn_cdc_get_all_changes_dbo_Customers (@from_lsn = sys.fn_cdc_get_min_lsn('dbo_Customers'), @to_lsn = sys.fn_cdc_get_max_lsn(), @row_filter_option = 'all'); GO |
This function will return all changes that have occurred on ‘Customers’ table between the lowest and highest log sequence numbers (LSNs). The last parameter @row_filter_option controls which rows are returned based on their change state (for example, whether they were inserted, updated, or deleted).
Conclusion
Tracking data changes in SQL Server doesn’t have to be a tedious process. By utilizing the built-in tools provided by SQL Server, such as Change Data Capture, you can easily monitor and track changes to your data, allowing you to stay ahead of any potential issues and keeping your database secure and efficient.
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-- Don't forget to disable CDC on the table and the database once you're done EXEC s<a href="mailto:ys.sp_cdc_disable_table @source_schema" >ys.sp_cdc_disable_table @source_schema</a> = 'dbo', @source_name = 'Customers', @capture_instance = 'dbo_Customers' GO EXEC sys.sp_cdc_disable_db GO |
In closing, CDC is a great tool that eases the burden of tracking changes in your data over time. It’s worth spending some time to understand it and incorporate it into your SQL Server toolbox. Happy Coding!