Associação de várias tabelas do MySQL

select
        ss.*,
        se.name as engine,
        ss.last_run_at + interval ss.refresh_frequency day as next_run_at,
        se.logo_name,
        pr.project_name -- +
from 
        searches ss
        join search_engines se on ss.engine_id = se.id
        join projects pr on ss.project_id = pr.id -- +
where
        ss.user_id='.$user_id.'
group by ss.id
order by ss.project_id, ss.domain, ss.keywords