如何修改这个语句

以下语句可以实现查询出动态时间段内每周的数据记录数，且得到的结果显示如下：
周期 记录数
1 50
2 35
3 100
4 67
............

set datefirst 1  
select datepart(wk,CAST(txtime AS DATETIME)) as 周,count(1) as 记录数
from qxzb
where CAST(txtime AS DATETIME)>='2011-01-01' and CAST(txtime AS DATETIME)<'2011-6-21'
group by datepart(wk,CAST(txtime AS DATETIME))


现要实现查询出动态时间段内每月的数据记录数(需自动识别每月的天数，如2月份从1日至28日)，且显示格式如下，请问如何修改？
周期 记录数
1 200
2 135
3 100
4 167
.............

set datefirst 1  
select 
DATEPART(MM,CAST(txtime AS DATETIME)) AS '月',datepart(wk,CAST(txtime AS DATETIME)) as 周,count(1) as 记录数
from qxzb
where CAST(txtime AS DATETIME)>='2011-01-01' and CAST(txtime AS DATETIME)<'2011-6-21'
group by datepart(wk,CAST(txtime AS DATETIME)),DATEPART(MM,CAST(txtime AS DATETIME))

SQL code

select convert(varchar(7),txtime,120) 月,count(1) 记录数
from qxzb
where CAST(txtime AS DATETIME)>='2011-01-01' and CAST(txtime AS DATETIME)<'2011-6-21'
group by convert(varchar(7),txtime,120)