Foreign Data Wrapper (FDW) is an extension available in PostgreSQL that allows you to access a table or schema in one database from another.
Postgres now has a lot of (foreign data wrappers)[https://wiki.postgresql.org/wiki/Foreign_data_wrappers] available and they work with plenty of different source types: NoSQL databases, platforms like Twitter and Facebook, geospatial data formats, etc.
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Your data may be segregated across databases, but still related in ways that makes being able to combine or aggregate it desirable.
- Eg: Authorization server 👨👨👦 user details compare it with resourece server