Nice article.

Note that there's more than one 'MySQL FOREIGN KEY' implementation. MySQL Ndb Cluster also supports foreign keys with some differences wrt the InnoDB implementation :

- NDB, therefore not limited to a single MySQL Server, shard etc - Not limited to references between tables in a single database - Supports NoAction deferred constraint checks - Cascaded changes Binlogged independently as part of RBR (Nice side effect of reducing replica apply time work) ...

https://dev.mysql.com/blog-archive/foreign-keys-in-mysql-clu...

Some of the issues described wrt DDL limitations are shared.

Many schemas seem to overuse foreign keys perhaps under the assumption that they are required for or accelerate joins?