Firebird applications can work with several databases at the same time through the client library – something that not all relational database systems allow. Tables from separate databases can not be joined to return linked sets, but cursors can be used to combine information.

If consistency across database boundaries is required, Firebird can manage output sets from querying multiple databases inside a single transaction. Firebird implements automatic two-phase commit when data changes occur, to ensure that changes cannot be committed in one database if changes in another database, within the same transaction context, are rolled back or lost through a network failure.