存储过程中参数输出的问题 ( 积分: 50 )

小弟遇到一个参数输出的问题，问题出在输入参数是real的问题上：
CREATE PROCEDURE dbo.sp_mc_rating
@mkt varchar(30),
@channelname varchar(10),
@target1 varchar(10),
@virtime real,
@spottime real,
@Rtg1 char(10)='' output
AS
declare @SQL varchar(8000)
set @SQL='select '''+(@Rtg1)+'''=cast('+@mkt+'.rating as char(10)) from '+@mkt+' where target='''+@target1+''' and channelname='''+@channelname+''' and daypart>'''+@virtime+''' and daypart<='''+@spottime+''''
exec(@SQL)
GO

问题就在@virtime和@spottime这两个变量在过程中应该怎么写。就差这一点点了，请指教
谢谢！

CREATE PROCEDURE dbo.sp_mc_rating
@mkt varchar(30),
@channelname varchar(10),
@target1 varchar(10),
@virtime real,
@spottime real,
@Rtg1 char(10)='' output
AS
declare @SQL varchar(8000)
set @SQL='select '''+(@Rtg1)+'''=cast('+@mkt+'.rating as char(10)) from '+@mkt+' where target='''+@target1+''' and channelname='''+@channelname+''' and daypart>'''+ Convert(nvarchar(20), @virtime) +''' and daypart<='''+ Convert(nvarchar(20), @spottime) +''''
exec(@SQL)
GO