放一个 sum() 围绕您当前的查询

select sum(c)
from
(
    select object, count(distinct user) 'c' 
    from events e 
    where (action = 'viewed') and object in ('car','truck') 
    group by object, 'c'
) tmp

只需简单一点就可以得到你想要的：

select count(*) 
from events e 
where action = 'viewed' 
and object in ('car','truck')

如果您希望按对象区分不同的用户，可以这样做

select count(*) 
from events e 
where action = 'viewed' 
  and object in ('car','truck') 
  and ROW_NUMBER() OVER (PARTITION BY Object, User) = 1