sqlserver 查询最近几天统计数，如果为空，则自动补全

select b.Date,count(a.id) as Num from (
--按照日期范围填补缺失日期
select convert(varchar(10),dateadd(day,number,'2020-12-20'),120) as [Date] from
master..spt_values
where number>=0 and type='p')b
left join
hk_order a
on Convert(varchar(10),a.createtime,120)=b.Date
where b.Date<getdate()
group by b.Date