Cascading Deletes of Database Rows in MySQL with Foreign Key Constraints

The good news is that you, as a PHP developer, can take advantage of the numerous advantages offered by foreign key constraints when working with InnoDB tables in MySQL (even though support for MyISAM tables has already been announced for future releases of MySQL).

So, if you’re interested in learning the basic concepts that surround the use of foreign key constraints in MySQL, then in this set of articles you’ll find an approachable guide to this topic. It's complemented with a decent variety of code samples aimed specifically at demonstrating how to maintain the integrity of a database when updating and deleting the rows of a parent table.

If you already read the article that precedes this one, then it’s highly probable that you now have a pretty clear idea of how to work with foreign key constraints when using InnoDB tables in MySQL. In that introductory part of the series, I explained how to trigger a cascading update operation on the records of a child table when the rows of the parent table were updated as well.

While describing this cascading updating process in plain English may sound a bit confusing and ambiguous, the truth is that translating it to functional SQL code is much easier than you might think. In its simplest version, the procedure is reduced to first creating a parent and a child table, defining a foreign key in the child, and then specifying what action will take place when updating the parent’s records. Period.

Undeniably, the major benefit to using foreign key constraints is that relationships between tables can be easily handled at the database level, instead of implementing the required logic within the application that interacts with the data layer. It's worth noting that this may be a detrimental factor in terms of performance, particularly when building large-scale programs.

Since database performance issues are certainly out of the scope of this article series, what I’m going to do in the next few lines will consist of demonstrating how to use foreign key constraints for triggering cascading deletions of records in a child table, where rows in the parent table are deleted too.

Want to see how this mix of buzzwords can be turned into clean SQL code? Then don’t hesitate anymore; start reading now!