Q:

Composite Primary Key having column with Allow Null true

I would like to know the best practice. 
I have a table Committee, Application, EmpInternal and EmpExternal 
The primary key of Committee is a composite Key comprising of ApplicationID, EmpInternalID and EmpExternalID
Now since, AllowNull property is not allowed to be true in a column in composite key. What should I do to store committee members in Committee  table which are sometimes Internal and external. All the columns ApplicationID, EmpInternalID and EmpExternalID are autonumber in their respective tables
CREATE TABLE [dbo].[Employee](
[EmployeeID] [varchar](10) NOT NULL,    
[UserID] [varchar](100) NULL,
[Title] [varchar](50) NULL,
[Name] [nvarchar](240) NULL,
[Rank] [varchar](150) NULL,
[Department] [varchar](240) NULL,
[College] [varchar](240) NULL,
[POBox] [varchar](120) NULL,
[Phone] [varchar](60) NULL,
[JoinDate] [varchar](200) NULL,
CONSTRAINT [PK_Employee1] PRIMARY KEY CLUSTERED 
(
[EmployeeID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) 

CREATE TABLE [dbo].[EmployeeExternal](
[EmployeeExID] [varchar](10) NOT NULL,  
[Title] [nvarchar](50) NULL,
[Name] [nvarchar](50) NULL,
[Rank] [nvarchar](50) NULL,
[Department] [nvarchar](4000) NULL,
[Organization] [nvarchar](4000) NULL,
[Address] [nvarchar](4000) NULL,
[Email] [nvarchar](50) NULL,
[Email2] [nvarchar](50) NULL,
[Phone] [nvarchar](50) NULL,
[Mobile] [nvarchar](50) NULL,
[Country] [nvarchar](50) NULL,
CONSTRAINT [PK_Employee1] PRIMARY KEY CLUSTERED 
  ( [EmployeeExID] ASC   )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE =  OFF, IGNORE_DUP_KEY = OFF,     ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) 

A:

A flag record in the Employee table and EmployeeExternal table is a better solution than merging these two tables. the key of flagged record in the composite key remove the use of null in the composite key 

