Having foreign keys between two different databases using linked servers?

Question

I have two databases that I have connected using linked servers.I have DB1 and DB2 which I only have read access to. I'm using DB1 for my application and have linked DB2 so I can combine queries. Is it possible to have foreign keys in DB1 that are linked to DB2?

Answer 1

No, it is not possible to create foreign keys between objects in different databases (even if they are on the same server). The official documentation is pretty clear about that:

FOREIGN KEY constraints can reference only tables within the same database on the same server. Cross-database referential integrity must be implemented through triggers. For more information, see CREATE TRIGGER (Transact-SQL) .

It even points you to the possible workaround, ie to try to implement some kind of referential integrity checks using triggers. You can add after insert/update triggers on both sides to validate the data changes, and after delete triggers on the primary table to check are there child records. If the validation fails, you will raise an error . You can also use instead of triggers .

But the solution with triggers will not guarantee the referential integrity anyway. You can lose connectivity between databases. You can restore one of the databases from older backup. All kind of things can go wrong. You better try to reconsider your database design. Is it possible to combine these two databases into one? Is it possible to maintain copies of both tables into each of the databases and try to replicate stuff?