Sql many to many relation with the same table - sql

Question

I want to create a table of users, lets name it USERS and I want that each
user will be able to point to more users. You can think of it as a user that have some friends who are also user, and have more friends that are also user and so on.
Do I need to use many to many relation between this table to itself or use a junction table?
For instance the table (without the notation of junction table) might look like:
| USER_ID(PK) | NAME | AGE | _ID(FK) |

Answer 1

You should use a junction table where each row contains details of a "relationship" between two users.
|UserID1|UserID2|
| 1| 2|
| 2| 3|

Answer 2

You need another table n:n where usersID's are saved, for example there would be for each friend of yours an record including yourId and onefriendsId

Answer 3

As you already mentioned, you have one object named 'User' and the other named 'Person'. These two have a Factory relation which means "Every 'Person' definitely is a 'User'" but "Every 'User' might not be a 'Person'", also means that "Every 'User' that is also 'Person' can have related 'Person's by using 'PersonOrder' as a junction table" and the other constraint is that as a junction table "Each child 'Person' must be unique".
I know that it's so far as you really need to implement, but it is a normalized structure. If I were you, I'd implement this way.
Link to Diagram: http://sdrv.ms/ROVtJc
Cheers
USE [temp]
GO
/****** Object: Table [dbo].[User] Script Date: 09/06/2012 17:11:23 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[User](
[Id] [bigint] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NOT NULL,
[Age] [tinyint] NOT NULL,
CONSTRAINT [PK_User] 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]
GO
/****** Object: Table [dbo].[Person] Script Date: 09/06/2012 17:11:23 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Person](
[Id] [bigint] NOT NULL,
CONSTRAINT [PK_Person] 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]
GO
/****** Object: Table [dbo].[PersonOrder] Script Date: 09/06/2012 17:11:23 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[PersonOrder](
[Id] [bigint] IDENTITY(1,1) NOT NULL,
[Person_Parent_Id] [bigint] NOT NULL,
[Person_Child_Id] [bigint] NOT NULL,
CONSTRAINT [PK_PersonOrder] 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],
CONSTRAINT [IX_FriendOrder_Child_Unique] UNIQUE NONCLUSTERED
(
[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]
GO
/****** Object: ForeignKey [FK_Person_User] Script Date: 09/06/2012 17:11:23 ******/
ALTER TABLE [dbo].[Person] WITH CHECK ADD CONSTRAINT [FK_Person_User] FOREIGN KEY([Id])
REFERENCES [dbo].[User] ([Id])
GO
ALTER TABLE [dbo].[Person] CHECK CONSTRAINT [FK_Person_User]
GO
/****** Object: ForeignKey [FK_PersonOrder_Person_Child] Script Date: 09/06/2012 17:11:23 ******/
ALTER TABLE [dbo].[PersonOrder] WITH CHECK ADD CONSTRAINT [FK_PersonOrder_Person_Child] FOREIGN KEY([Person_Parent_Id])
REFERENCES [dbo].[Person] ([Id])
GO
ALTER TABLE [dbo].[PersonOrder] CHECK CONSTRAINT [FK_PersonOrder_Person_Child]
GO
/****** Object: ForeignKey [FK_PersonOrder_Person_Parent] Script Date: 09/06/2012 17:11:23 ******/
ALTER TABLE [dbo].[PersonOrder] WITH CHECK ADD CONSTRAINT [FK_PersonOrder_Person_Parent] FOREIGN KEY([Person_Child_Id])
REFERENCES [dbo].[Person] ([Id])
GO
ALTER TABLE [dbo].[PersonOrder] CHECK CONSTRAINT [FK_PersonOrder_Person_Parent]
GO