SELECT
    species.id
FROM
    encyclopedia.species
JOIN
    encyclopedia.common_names ON (common_names.owner_id = species.id AND common_names.owner_type = 'Species')
WHERE
    species.name ILIKE E'%gavia%' OR common_names.name ILIKE E'%gavia%'
GROUP BY
    species.id
ORDER BY
    COALESCE(common_names.name, species.name);