Si desea los valores en una sola fila, puede hacer esto:
select max(playtime), min(playtime), avg(playtime)
from yourtable
group by mediaid;
Si los quiere en filas separadas, use un UNION ALL :
select max(playtime) playtime, mediaid, 'Max' Type
from yourtable
group by mediaid
union all
select min(playtime) playtime, mediaid, 'Min'
from yourtable
group by mediaid
union all
select avg(playtime) playtime, mediaid, 'Avg'
from yourtable
group by mediaid
order by mediaid, playtime;
ver SQL Fiddle con demostración
Edición n.° 1, utilizando los datos de muestra agregados:
select m.medTitle,
min(TIMESTAMPDIFF(SECOND, s.dmtViewStart, s.dmtViewEnd)) playtime
from tbldoctormediatracktest s
left join tblmedia m
on s.MedId = m.MedId
group by m.medTitle
union all
select m.medTitle,
avg(TIMESTAMPDIFF(SECOND, s.dmtViewStart, s.dmtViewEnd)) playtime
from tbldoctormediatracktest s
left join tblmedia m
on s.MedId = m.MedId
group by m.medTitle
union all
select m.medTitle,
max(TIMESTAMPDIFF(SECOND, s.dmtViewStart, s.dmtViewEnd)) playtime
from tbldoctormediatracktest s
left join tblmedia m
on s.MedId = m.MedId
group by m.medTitle
order by medTitle, playtime
