Liquibase，在Oracle中创建外键，前提条件

I have a production and a QA instance of my application into which I'm integrating Liquibase. This means DDL and data already exists (or not if on development box). I have to create a changeLog which records everything as RAN on the non-empty DBs but execute actually on empty DBs. I'm on a good way but I'm a bit stuck with creating the foreign keys. (the database is Oracle).I have a production and a QA instance of my app