PostgreSQL Accessing multiple database from stored function

I want to access different databases from postgresql stored functions.

For example:

CREATE O开发者_开发问答R REPLACE FUNCTION test ()  RETURNS SETOF volume AS
$BODY$

SELECT * FROM db2.volume
ORDER BY db2.volume.volumeID

$BODY$  
LANGUAGE sql STABLE  
COST 100  
ROWS 1000;

any input will be great help.

Regards, Manasi

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what you need is database link