关于变量赋值的问题，请教大家！

CREATE PROC NC_RPT

@MON VARCHAR(6),@B datetime

AS

SET ANSI_NULLS ON

SET ANSI_NULLS ON 

DECLARE @QF VARCHAR(8000)

select @B=acct_month from acct_month where acct_month1='+CAST(@MON AS VARCHAR)+'

/*这里acct_month 表中有两个字段，分别是acct_month datetime型　和acct_month1字符型，为的是能够让用户输入

一个年月比如'200901' 而得到一个datetime型的值赋给@B,其目的是为了能够使用下面语句中的dateadd函数为其做年月的加减*/

SET @QF='

IF EXISTS (SELECT * FROM SYSOBJECTS WHERE NAME=''NCRPT2_'+CAST(@MON AS VARCHAR)+''')

BEGIN 

DROP TABLE NCRPT2_'+CAST(@MON AS VARCHAR)+'

select @B=acct_month from acct_month where acct_month1='+CAST(@MON AS VARCHAR)+'

SELECT REGION_NAME,sum(charge) AS [B2]

INTO NCRPT2_'+CAST(@MON AS VARCHAR)+'  FROM  

acct_item_'+CAST(@MON AS VARCHAR)+'_t where acct_month=CONVERT(VARCHAR(6),DATEADD(MONTH,-1,@B),112) 

group by region_name

END 

ELSE 

SELECT REGION_NAME,sum(charge) AS [B2]

INTO NCRPT2_'+CAST(@MON AS VARCHAR)+'  FROM  

acct_item_'+CAST(@MON AS VARCHAR)+'_t where acct_month=CONVERT(VARCHAR(6),DATEADD(MONTH,-1,@B),112) 

group by region_name

'

EXEC(@QF)

GO