来自不同数据库模式的表的ERD

I have got various database schemas on a server in oracle sql and when I run the database sql modeler to get the ERD diagram it's showing me the table connections within the different database schemas only and not across tables in different schemas. However, I was asked to pull out data from tables which have common keys for joining from the various databases schemas. However, the ERD diagram is not showing these connections. Is there any way one can identify which tables from the various schemas have common primary/foreign keys and can be connected? I have got various database schemas on a server