插入语句：
insert into qualitys (lu,ru,ld,rd,s_time,o_doctorunit,o_doctor,o_sick,o_producttype,o_mainstuff,o_no) values ('','','6','','2012-03-18','惠爱口腔','田医生','曹光辉','钴铬金属冠','','JC005779')
表结构SQL语句：
USE [dental_web]
GO
/****** 对象: Table [dbo].[qualitys] 脚本日期: 04/04/2012 14:09:25 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[qualitys](
[upldate] [datetime] NULL CONSTRAINT [DF_qualitys_upldate] DEFAULT (getdate()),
[lu] [varchar](20) COLLATE Chinese_PRC_CI_AS NULL,
[ru] [varchar](20) COLLATE Chinese_PRC_CI_AS NULL,
[ld] [varchar](20) COLLATE Chinese_PRC_CI_AS NULL,
[rd] [varchar](20) COLLATE Chinese_PRC_CI_AS NULL,
[s_time] [datetime] NULL,
[o_doctorunit] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL,
[o_doctor] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL,
[o_sick] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL,
[o_producttype] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL,
[o_mainstuff] [nvarchar](200) COLLATE Chinese_PRC_CI_AS NULL,
[o_no] [varchar](20) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
GO
SET ANSI_PADDING OFF
数据插入后nvarchar的字段内容显示为???或????，字数不同，?号不等 。
谢谢是怎么回事？谢谢。
