Social media has revolutionized the way we connect with others, creating an Always Connected World. However, sometimes this constant connectivity can lead to unexpected issues, as my friend recently discovered.

One day, my friend noticed that rows were mysteriously disappearing from their product details table. They were unable to determine the cause, as they had removed any code that referenced the table and ensured that no DELETE commands were executed. They even suspected intrusion or a virus.

Curious about the problem, I decided to investigate. After asking questions about audit, policy management, and profiling the data, I quickly realized that the issue was not as complex as it seemed. There was no intrusion, SQL Injection, or virus problem. Instead, the problem stemmed from the use of foreign keys with ON UPDATE CASCADE and ON DELETE CASCADE.

When a foreign key is created with ON DELETE CASCADE, it means that if a row with a key referenced by foreign keys in other tables is deleted, all rows containing those foreign keys will also be deleted. Similarly, ON UPDATE CASCADE specifies that if a key value in a row is updated and is referenced by foreign keys in other tables, all of the foreign key values will also be updated to the new value.

In my friend’s case, they had two tables: Products and ProductDetails. They had created a foreign key relationship between the two tables based on the product ID. When they updated their catalog, they would delete products that were no longer available. However, due to the ON DELETE CASCADE, the corresponding rows in the ProductDetails table were also deleted.

This behavior is correct and expected. SQL Server is behaving as it should. The problem was not with the database engine, but with the understanding and implementation of the business logic. In this case, my friend needed a Product Master Table, a Current Product Catalogue, and a Product Order Details History table. By using only two tables and not properly understanding the relationship between them, they encountered cascading delete issues.

A possible workaround for this situation would have been to use a soft delete approach. Instead of actually deleting the record, they could have hidden it from the original product table. This would have prevented the cascading delete problem.

In future blog posts, I will delve into the design implications and other related issues. For now, it’s important to remember that sometimes we are our own worst enemy. This situation serves as a great example of that.

Stay tuned for tomorrow’s blog post, where we will examine their code and explore potential workarounds. Feel free to share your opinions, experiences, and comments.