Use:
Count(case when a.photoappimage is null then 1 end) as via_u,
Count(case when a.photoappimage is null then 1 end)/100. as via_u_pct,
Count(case when a.photoappimage=1 then 1 end ) as via_p,
Count(case when a.photoAppImage is null or a.photoAppImage=1 then 1 end) as via_u_or_p
Update: combining all (and use a subquery to simplify pct calculation):
select
storeId,
district,
region,
via_u,
via_p,
via_u/100./(via_u+via_p) as via_u_pct
from (
select
a.storeId, b.district, b.region,
count (case when a.photoAppImage is null then 1 end) as via_u,
count (case when a.photoAppImage =1 then 1 end) as via_p
from
used_listings_V2 a
left outer join
locations b on a.storeId = b.storeID
where
convert(date, a.imageUpdateDate) = convert(date, GETDATE()-1)
group by
a.storeId, b.district, b.region
) Step1
13
solved difficulty giving aliases inside case statement