Most MySQL applications don't use FKs. The world keeps turning. Besides performance issues, FKs cause ordering issues with restoring tables when necessary. Ho

Most MySQL applications don't use FKs. The world keeps turning. Besides performance issues, FKs cause ordering issues with restoring tables when necessary. However, they're great for diagramming tools to show table relationships. I'm more concerned when I don't see unique indexes on things that need to be unique (often caused by early versions of RoR.) In my experience, this is never a theoretical problem - it always becomes a major operational problem. Source: MySQL DBA