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Enforce Referential Integrity with mismatched primary keys

Posted on 2010-11-23
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Last Modified: 2012-05-10
Hi,

Scenario 1:
On table 1 you have 3 primary keys, on table 2 you reference table 1's primary keys through a foreign key and thereby enforcing referential integrity. All Good.

Scenario 2 which I'm trying to get right:
On table 1 you have 3 primary keys but on table 2 you only have 2 fieldS that match table 1's primary keys.  Is there an elegant way to enforce referential integrity?

I get that you can do it through a trigger, but it's too easy to disable a trigger so I'm aiming for something more hardcore like a foreign key.

I'm trying to get something like this to work:
ALTER TABLE [dbo].[TABLE2]  WITH CHECK ADD  CONSTRAINT [CYFOK3_TB2] FOREIGN KEY([TB2_PAGE], [TB2_TAB])
REFERENCES [dbo].[TABLE1] ([TB1_PAGE], [TB1_TAB])

ALTER TABLE [dbo].[TABLE2] CHECK CONSTRAINT [CYFOK3_TB2]

Thanks      
CREATE TABLE [dbo].[TABLE1](
	[TB1_PAGE] [nvarchar](6) NOT NULL,
	[TB1_TAB] [nvarchar](15) NOT NULL,
	[TB1_STATE] [nvarchar](12) NOT NULL DEFAULT ('*'),
	[TB1_SQLIDENTITY] [int] IDENTITY(1,1) NOT NULL,
	CONSTRAINT [CYPRIK_TB1] PRIMARY KEY NONCLUSTERED 
	(
		[TB1_PAGE] ASC,
		[TB1_TAB] ASC,
		[TB1_STATE] ASC
	)
	WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) 
	ON [PRIMARY],
	CONSTRAINT [CYUNQSQL_TB1] UNIQUE NONCLUSTERED 
	(
		[TB1_SQLIDENTITY] 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


CREATE TABLE [dbo].[TABLE2](
	[TB2_PAGE] [nvarchar](6) NOT NULL,
	[TB2_TAB] [nvarchar](15) NOT NULL,
	[TB2_SQLIDENTITY] [int] IDENTITY(1,1) NOT NULL,
	CONSTRAINT [CYPRIK_TB2] PRIMARY KEY NONCLUSTERED 
	(
		[TB2_PAGE] ASC,
		[TB2_TAB] ASC
	)
	WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) 
	ON [PRIMARY],
	CONSTRAINT [CYUNQSQL_TB2] UNIQUE NONCLUSTERED 
	(
		[TB2_SQLIDENTITY] 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

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Question by:Cyber-Storm
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6 Comments
 
LVL 143

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 300 total points
ID: 34196373
if you have this kind of "design", the design is wrong aka not normlized.
you are likely missing some intermediate table, in your case, a table with indeed only the 2 columns as primary key, and table1 having the 2 fields (of the 3 being primary key) to be a foreign key to that table ...
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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 34196378
and to answer the question: a foreign key points to a primary key. you cannot have a foreign key point to a partial part of the primary key of the other table ...
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LVL 6

Accepted Solution

by:
subhashpunia earned 200 total points
ID: 34196423
You can add another foreign key on Table1 on two columns refering to the two columns of Table1 like:

ALTER TABLE [dbo].[TABLE1]  WITH CHECK ADD  CONSTRAINT [CYFOK3_TB1] UNIQUE ([TB2_PAGE], [TB2_TAB])
GO
ALTER TABLE [dbo].[TABLE2]  WITH CHECK ADD  CONSTRAINT [CYFOK3_TB2] FOREIGN KEY([TB2_PAGE], [TB2_TAB])
REFERENCES [dbo].[TABLE1] ([TB1_PAGE], [TB1_TAB])
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Author Comment

by:Cyber-Storm
ID: 34196539
@angel, none of that is helping any :(
I'm trying to establish referential integrity hence no you didn't answer the question. I know what a foreign key and primary key is, I was trying to offer an example.  Maybe I shouldn't be so "complete" in my explanations since the more I offer, the more you "geniuses" take things out of context

@subhash
Thanks, I thought of that too, but I would that not then prevent me from adding a state?  See it must be able to handle a page, tab and state on table 1, but table 2 only needs to refer to a page and a tab since it doesn't care about the state.

---

Table 1:
Page1, Tab1, State1
Page1, Tab1, State2
Page1, Tab2, State1
Page1, Tab2, State2
Page2, Tab1, State1
Page2, Tab2, State1
etc

Table 2:
Page1, Tab1 = Table1.Page1, Table1.Tab1, Table1.State1 and Table1.Page1, Table1.Tab1, Table1.State2
etc

I can add a trigger that will check that page and tab exists in table 1 before allowing an insert, update or delete.  But I was hoping for a more elegant solution to enforcing referential integrity like a foreign key constraint does natively.

Hope this adds a little more useful information for you guys.

Thanks,
Storm
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LVL 143

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 300 total points
ID: 34196587
I can only repeat: unless you have a primary key on PageX and TabX somewhere, you cannot have a foreign key pointing to it. full stop.
That's the way PK <=> FK works, and as you say, you are already aware of that.

this does not result as a limitation of the syntax, but is a result of the "requirement" of where it comes from: which is normalization rules.

you can use a trigger to validate the existence, indeed.

note:
>On table 1 you have 3 primary keys
is actually wrong wording (might be language barrier ...)
the correct wording would be:
on table 1 there is 1 primary key over 3 columns

CHeers
0
 

Author Closing Comment

by:Cyber-Storm
ID: 34196676
Based on the 3 selected answers I was able to figure out my problem and implement an elegant solution.

Thanks guys :)
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