关于统计关闭率的问题

[itfamily]

现有表question如下：
id description createdate state
1 aaa 2015-03-01 0
2 bbb 2015-03-05 0
3 ccc 2015-03-07 1
4 ddd 2015-03-11 0
5 eee 2015-03-21 1
6 fff 2015-04-01 0

字段state 0表示未关闭，1表示已关闭


我想统计2015-03月份的问题关闭率(已关闭问题/所有问题 *100%)，请问如何实现？

[jamesrggg]

Select (SUM(Case State When 0 Then 0 Else 1 End)*100.0)/(COUNT(1)*1.0) From question Where createdate Between N'2015-03-01' And N'2015-03-31'

[还在加载中灬]

SELECT
	CONVERT(VARCHAR(7),createdate,120)
	,SUM(CASE WHEN STATE=1 THEN 1 ELSE 0 END)*1.0/COUNT(id)[关闭率]
FROM question
WHERE createdate>='2015-03-01'AND createdate<'2015-04-01'
GROUP BY CONVERT(VARCHAR(7),createdate,120)