sql语句，获取2016年7月份，每日任务数量

SELECT COUNT(*) as count, CONVERT(char(10),AssignDate,121) as day
FROM [BlogTask].[dbo].[Task]
where AssignDate is not null
and AssignDate between '2016-07-01' and '2016-07-31'
group by CONVERT(char(10),AssignDate,121)