一个表的两个外键都指向自己
我看到一段SQL,很不理解一个表为什么要建两个都指向自己的外键。。。
CREATE TABLE [dbo].[tblSession](
[iUniqueId] [int] IDENTITY(1,1) NOT NULL,
[iUserUniqueId] [int] NOT NULL,
[nvcSessionId] [nvarchar](100) NOT NULL,
[dtSessionStartTime] [datetime] NOT NULL,
[dtSessionEndTime] [datetime] NULL,
[bSessionInProgress] [bit] NOT NULL,
CONSTRAINT [PK_tblSession] PRIMARY KEY CLUSTERED
(
[iUniqueId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[tblSession] WITH CHECK ADD CONSTRAINT [FK_tblSession_tblSession] FOREIGN KEY([iUniqueId])
REFERENCES [dbo].[tblSession] ([iUniqueId])
GO
ALTER TABLE [dbo].[tblSession] CHECK CONSTRAINT [FK_tblSession_tblSession]
GO
ALTER TABLE [dbo].[tblSession] WITH CHECK ADD CONSTRAINT [FK_tblSession_tblSession1] FOREIGN KEY([iUniqueId])
REFERENCES [dbo].[tblSession] ([iUniqueId])
GO