SQL中以日期为条件统计方法

 /*统计每天数据总量三种方法：
        select convert(char(10),happentime ,120) as date ,count(1) from table1
        group by convert(char(10),happentime ,120) order by date desc
       select day(happentime) as date,count(*) from  table1 
       group by day(happentime) order by date desc
         SELECT left([happentime],5),count (1)
         from [database].[dbo].[ table1]
         group by left([happentime],5)
         order by left([happentime],5)
说明：happentime为表字段名;
大家分别测试下 left([happentime],20)  与 convert(char(10),happentime ,120) 、day(happentime) 两者的区别，对于新人来说，从left([happentime],5) 来看结果往往看不出来与其他两个的不同。
如果不明白语句如何写，请参考如下:
select convert(char(10),happentime ,120) from table1
SELECT left([happentime],5) from table1
SELECT left([happentime],5) from table1