use two primary keys attribute from a table with different title - sql

Question

I got table "Functions" with Function_ID {PK} and I want another table "Hierarchy" with Hierarchy_ID {PK} which defines tree structure of functions so i need one Function_ID from Function table AS Parent_ID and one Function_ID AS Child. my question is how i can use two primary keys from another table to make it together as Foreign key
I am using SQL Server 2012 and the Management Studio
Many Thanks

Answer 1

Actually you just need to add a ParentFunction_ID column in the Functions table.
You don't need another table if your structure is indeed a tree.
Then make the ParentFunction_ID to be a FK to the same table Functions.
So ParentFunction_ID (FK) would be pointing to Function_ID (PK).
The only record which has ParentFunction_ID NULL would be the root of your tree.
Here is some sample code:
USE [test]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[Functions](
[Function_ID] [int] IDENTITY(1,1) NOT NULL,
[FunctionCode] [varchar](max) NULL,
[ParentFunction_ID] [int] NULL,
CONSTRAINT [PK_Functions] PRIMARY KEY CLUSTERED
(
[Function_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
SET ANSI_PADDING OFF
GO
ALTER TABLE [dbo].[Functions] WITH CHECK ADD CONSTRAINT [FK_Functions_Functions] FOREIGN KEY([ParentFunction_ID])
REFERENCES [dbo].[Functions] ([Function_ID])
GO
ALTER TABLE [dbo].[Functions] CHECK CONSTRAINT [FK_Functions_Functions]
GO

Answer 2

Name your Functions table a Function table. AFAIK using
plurals for table names is not really a good practice.
So you can do this.
--- 1 ---
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[Function](
[Function_ID] [int] IDENTITY(1,1) NOT NULL,
[FunctionCode] [varchar](max) NULL,
CONSTRAINT [PK_Function] PRIMARY KEY CLUSTERED
(
[Function_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
SET ANSI_PADDING OFF
GO
--- 2 ---
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Hierarchy](
[ID] [int] IDENTITY(1,1) NOT NULL,
[ParentFunction_ID] [int] NULL,
[ChildFunction_ID] [int] NULL,
CONSTRAINT [PK_Hierarchy] 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
ALTER TABLE [dbo].[Hierarchy] WITH CHECK ADD CONSTRAINT [FK_Hierarchy_Function] FOREIGN KEY([ParentFunction_ID])
REFERENCES [dbo].[Function] ([Function_ID])
GO
ALTER TABLE [dbo].[Hierarchy] CHECK CONSTRAINT [FK_Hierarchy_Function]
GO
ALTER TABLE [dbo].[Hierarchy] WITH CHECK ADD CONSTRAINT [FK_Hierarchy_Function1] FOREIGN KEY([ChildFunction_ID])
REFERENCES [dbo].[Function] ([Function_ID])
GO
ALTER TABLE [dbo].[Hierarchy] CHECK CONSTRAINT [FK_Hierarchy_Function1]
GO