select c.*,i.id as i_id,i.i_name,t.c_info_count
from (class c
left join info i on i.i_cid = c.id)
left join (
  select i_cid,count(id) as c_info_count from info group by i_cid
) t on t.i_cid = c.id
where c.c_pid = 0
and (
  i.id = (
    select top 1 id from info where i_cid = c.id order by id desc
  ) or i.id is null
)

select c.*,i.id as i_id,i.i_name,t.c_info_count
from (class c
left join (
  select i3.* from (
    select i_cid,max(id) as i_id_max
    from info group by i_cid) i2
    left join info i3 on i3.id = i2.i_id_max
  ) i on i.i_cid = c.id
)
left join (
  select i_cid,count(id) as c_info_count from info group by i_cid
) t on t.i_cid = c.id
where c.c_pid = 0