select
case when sign(imgid - 4) > 0 then 'next' else 'prev' end as dir,
case when sign(imgid - 4) > 0 then min(imgid) else max(imgid) end as imgid
from acores_imagens where imguser=1 and imgid <> 4
group by sign(imgid - 4)
order by sign(imgid - 4);