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)
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