No to mention that most SQL databases have complex consistency rules. Just checking that the target row exists (or not) before adding (or deleting) a record may

No to mention that most SQL databases have complex consistency rules. Just checking that the target row exists (or not) before adding (or deleting) a record may not result in a correct database state in the face of concurrent transactions. You better very carefully read your database's concurrency guarantees and ensure that all transactions are running with the right consistency level otherwise you will have a bad day. On top of that the JOIN method of following foreign keys often leads to missing rows if expected keys don't exist which can be very hard to debug.