create type fkey_desc as (
        table_name text,
        table_att  text,
        ref_table_name text,
        ref_att  text
);
create or replace function get_fkey_names (_name text) returns setof fkey_desc as $$
DECLARE
        _tmp     record;
        _i       int;
        _k       int;
        _l       int;
        _names   fkey_desc;
        _tab_name text;
        _ref_tab text;
BEGIN
        select into _tmp * from pg_constraint where conname = _name;
        _tab_name := relname from pg_class where oid = _tmp.conrelid;
        _ref_tab  := relname from pg_class where oid = _tmp.confrelid;
        for _i in  1 ..array_upper(_tmp.conkey,  1 ) LOOP
         _k := _tmp.conkey[_i];
         _l := _tmp.confkey[_i];
         select into _names
              _tab_name as table_name,
              (select attname from pg_attribute pga1 where attrelid = _tmp.conrelid AND attnum = _k LIMIT  1 ) as table_att,
              _ref_tab as ref_table_name,
              (select attname from pg_attribute pga2 where attrelid = _tmp.confrelid AND attnum = _l LIMIT  1 ) as ref_att;
         return next _names;
        END LOOP;
        return;
END
$$ language 'plpgsql';
-- работает примерно так:
select * from get_fkey_names('content_parent_id_fkey');
 table_name | table_att |  ref_table_name   | ref_att
------------+-----------+-------------------+---------
 content    | parent_id |  content          | node_id