关于sql server CONSTRAINT 在hibernate中配置问题

从来没用过CONSTRAINT，它在这儿什么意思呢 在hibernate 中怎么配置呢？
CREATE TABLE [dbo].[SMS_UPLOAD_INFO](
[Id] [bigint] IDENTITY(1,1) NOT NULL,
[Smsid] [varchar](20) NULL,
[good_name] [varchar](50) NULL,
[good_abledate] [smallint] NULL CONSTRAINT [DF_SMS_UPLOAD_INFO_good_abledate]  DEFAULT ((365)),
[Uptime] [datetime] NULL CONSTRAINT [DF_SMS_UPLOAD_INFO_Uptime]  DEFAULT (getdate()),
[Message] [varchar](280) NULL,
[Sendflag] [smallint] NULL CONSTRAINT [DF_SMS_UPLOAD_INFO_Sendflag]  DEFAULT ((0)),
[Address] [varchar](50) NULL,
[Phone] [varchar](50) NULL,
[Imgpath] [varchar](50) NULL CONSTRAINT [DF_SMS_UPLOAD_INFO_Imgpath]  DEFAULT (''),
[Flag] [smallint] NULL CONSTRAINT [DF_SMS_UPLOAD_INFO_Flag]  DEFAULT ((8)),
 CONSTRAINT [PK_SMS_UPLOAD_INFO] PRIMARY KEY CLUSTERED 
(
[Id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]