数据库架构：如果一个表是另一个表的一部分怎么办

我的 SQL Server 数据库有一个名为 Lead 的初始表。该表包含有关领导者的各种信息。它有 3 个外键列：IndustryId、BusinessTypeId 和 ReferenceId。我在有关表 Lead 和 Reference 的体系结构中遇到问题。

这是表 Lead 的脚本：

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[Lead](
    [LeadId] [int] IDENTITY(1,1) NOT NULL,
    [LeadName] [nvarchar](100) NOT NULL,
    [CompanyName] [nvarchar](100) NOT NULL,
    [Phone] [nvarchar](50) NOT NULL,
    [Address] [nvarchar](max) NOT NULL,
    [DOB] [date] NULL,
    [IndustryID] [int] NOT NULL,
    [BusinessTypeID] [int] NOT NULL,
    [IsDeleted] [bit] NOT NULL CONSTRAINT [DF_Lead_IsDeleted]  DEFAULT ((0)),
    [ReferenceId] [int] NOT NULL,
    [IsLead] [bit] NOT NULL,
    [Email] [nvarchar](100) NOT NULL,
    [Website] [nvarchar](100) NOT NULL,
    [RepresentativeName] [nvarchar](100) NOT NULL CONSTRAINT [DF_Lead_RepresentativeName]  DEFAULT (''),
    [IsClosed] [bit] NOT NULL CONSTRAINT [DF_Lead_IsClosed]  DEFAULT ((0)),
    [feedback] [bit] NOT NULL CONSTRAINT [DF_Lead_feedback]  DEFAULT ((0)),
    [feedbackMemo] [nvarchar](100) NULL,
 CONSTRAINT [PK_Lead] PRIMARY KEY CLUSTERED 
(
    [LeadId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO

ALTER TABLE [dbo].[Lead]  WITH CHECK ADD  CONSTRAINT [FK_Lead_LeadIndustry] FOREIGN KEY([IndustryID])
REFERENCES [dbo].[Industry] ([IndustryId])
GO

ALTER TABLE [dbo].[Lead] CHECK CONSTRAINT [FK_Lead_LeadIndustry]
GO

ALTER TABLE [dbo].[Lead]  WITH CHECK ADD  CONSTRAINT [FK_Lead_LeadReference] FOREIGN KEY([ReferenceId])
REFERENCES [dbo].[Reference] ([ReferenceId])
GO

ALTER TABLE [dbo].[Lead] CHECK CONSTRAINT [FK_Lead_LeadReference]
GO

ALTER TABLE [dbo].[Lead]  WITH CHECK ADD  CONSTRAINT [FK_Lead_LeadType] FOREIGN KEY([BusinessTypeID])
REFERENCES [dbo].[BusinessType] ([BusinessTypeId])
GO

ALTER TABLE [dbo].[Lead] CHECK CONSTRAINT [FK_Lead_LeadType]
GO

这是有问题的表的脚本参考：

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[Reference](
    [ReferenceId] [int] IDENTITY(1,1) NOT NULL,
    [ReferenceName] [nvarchar](100) NOT NULL,
    [Address] [nvarchar](max) NOT NULL,
    [DOB] [date] NULL,
    [Memo] [nvarchar](max) NOT NULL,
    [IsDeleted] [bit] NOT NULL,
    [Phone] [nvarchar](100) NOT NULL,
    [DateTimeAdded] [datetime] NOT NULL,
    [AddedByUserId] [int] NOT NULL,
    [DateTimeUpdated] [datetime] NULL,
    [UpdatedByUserId] [int] NOT NULL,
 CONSTRAINT [PK_Reference] PRIMARY KEY CLUSTERED 
(
    [ReferenceId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO

问题是每个 Lead 都有一个 Reference，但 Reference 可能是一个 Lead。在添加新线索时的 UI 中，要求用户设置其引用，但他可以选择现有线索作为引用新线索的线索，也可以选择普通引用。

所以现在我不确定，设置这些表的最佳方法是什么？我应该将它们合并到一个表 Lead 中，当它是一个简单的 Reference 时，我将不需要的列保留为 Null，还是保留两个表并向 Reference 表“LeadId”添加一个新列而不使其成为外键？或者也许是另一种方法。请指教。