给SQL平添月份参数

----------Convert(nvarchar(7),t1.StateDate,120)as StateMonth 下面的SQL 把日期转换成月份 有点不安全，希望能改进ALTER proc [dbo].[P_Prod_PoAndSalesMonth]  (--希望改成只能输入月份  @datetime varchar(30)='') as  begin     declare @cur_datetime varchar (30)--本月初始化时间    select @cur_datetime=case when @datetime = '' or @datetime is null then  CONVERT(datetime,CONVERT(char(8),getdate(),120)+'1')    else CONVERT(datetime,CONVERT(char(8),cast(case when len(@datetime)=7 or len(@datetime)=6 then @datetime+'-01'     else @datetime end as datetime),120)+'1') end       create table #rep (Id  int identity(1,1),                 --序列号  SkuNo                 varchar(60),                       --商品编号  ProductName           varchar(100),                      --商品名称  StateMonth            varchar(30),  )  --上月的数据汇总到临时表#t1    select t2.SkuNo,t2.ProductName,  Convert(nvarchar(7),t1.StateDate,120)as StateMonth--新加了一个字段月份   into #t1 from Wms_StockDailyState as t1  left join V_Prod_Sku t2 on t1.SkuId=t2.SkuId  where  ----参数@datetime    --这里希望月份大于上月初，小于本月  --State>'2012-5 and state<'2012-7' 或者是State>'2012-05 and state<'2012-07'  Convert(nvarchar(7),t1.StateDate,120)>'2012-5' and  Convert(nvarchar(7),t1.StateDate,120)<'2012-7'   group by t2.SkuNo,t2.ProductName,Convert(nvarchar(7),StateDate,120)     --本月的数据汇总到临时表#t2   select t2.SkuNo,t2.ProductName,Convert(nvarchar(7),t1.StateDate,120)as StateMonth    into #t2 from Wms_StockDailyState as t1  left join V_Prod_Sku t2 on t1.SkuId=t2.SkuIdwhere --这里改成 大于 本月初 ，小于本月末--也就是大于'2012-07'或者 2012-8  --StateDate>=@cur_datetime  and StateDate<dateadd(month,1,@cur_datetime )  --Convert(nvarchar(7),t1.StateDate,120)=@datetime  group by t2.SkuNo,t2.ProductName,Convert(nvarchar(7),t1.StateDate,120) select * from #rep end