select convert(varchar,a.d,111) as [日期],
isnull(b.qty,0) as [销量]
  from 
(
---生成时间段内所有的天数
select dateadd(day,number,'2020-04-19') as d from master..spt_values 
where type='p' 
and number >=0 
and dateadd(day,number,'2020-04-19') between '2020-04-19' and dateadd(day,0,'2020-04-23')


) as a 
left join 
(
 ---按天汇总的销量数据
 select convert(varchar,addtime,111) as d,count(id) as qty from Visiting_Log group by  convert(varchar,addtime,111)
) as b 
 on  convert(varchar,a.d,111) = b.d