Data is not always in one location only. More often than not, data is spread all over the infrastructure and it can be that data residing in various places which has to be integrated.
The solution to the problem is a foreign data wrapper, as defined by the SQL/MED standard.
In this section, the postgres_fdw extension will be discussed. It is a module that allows you to dynamically fetch data from a PostgreSQL data source. The first thing is to deploy the foreign data wrapper:
test=# \h CREATE FOREIGN DATA WRAPPER Command: CREATE FOREIGN DATA WRAPPERDescription: define a new foreign-data wrapperSyntax:CREATE FOREIGN DATA WRAPPER name[ HANDLER handler_function | NO HANDLER ][ VALIDATOR validator_function ...