dblink_get_pkey
provides information about the primary
key of a relation in the local database. This is sometimes useful
in generating queries to be sent to remote databases.
Name of a local relation, for example foo or myschema.mytab. Include double quotes if the name is mixed-case or contains special characters, for example "FooBar"; without quotes, the string will be folded to lower case.
Returns one row for each primary key field, or no rows if the relation has no primary key. The result rowtype is defined as
CREATE TYPE dblink_pkey_results AS (position int, colname text);