UNION, UNION ALL kullanarak yapabilirsin. Temp table kullanarakta yapabilirsin.

select country, GETDATE(), COUNT(host_name) as 'Downloads', '0' as 'Premium' from sites
union all
select country, GETDATE(), '0' as 'Downloads', COUNT(country) as 'Premium' from transactions
Temp table ile;

create table #tempTable
( 
Country nvarchar(250), DateOnly datetime, Downloads int, Premium int
)

insert into #tempTable (Country, DateOnly, Downloads, Premium)


select country, GETDATE(), COUNT(host_name) as 'Downloads', '0' as 'Premium' from sites
union all
select country, GETDATE(), '0' as 'Downloads', COUNT(country) as 'Premium' from transactions

select * from #tempTable
drop table #tempTable