Jared,
Yeah, It may be just a design issue but not quite sure.
I was referencing from a document "Data Modeling: It's Really All About the
Relationships" by Dr. Bert Scalzo of Quest Software.
Data modeling is part of the conceptual design phase. When speaking of the
E-R methodology, the data model produces 1. E-R diagram which represents
the data structures in some type of graphical form.
The second component is the data document which details the data objects,
relationships, and database rules. Here is where I think it could be argued
both a modeling/design issue. I certainly see some merit in your
reasoning. I agree the use of surrogate keys
would prevent this. I do not know why this was not mentioned by the author.
Rick
Jared.Still@ra
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10/30/2002
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Rick,
This doesn't actually have anything to do with data modeling,
but rather, database design.
The FK can't be enforced on a multipart key if one of the columns
is null, obviously. At least, I *think* it's obvious.
What happen when you try to update column b in table 2 with
a valid value?
with and invalid value?
There's a good case here for using surrogate keys, as always.
That way, invalid values cannot be put in an FK column, since there
is only one column needed to reference the foreign PK.
Jared
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10/30/2002 08:08 AM
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To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
cc:
Subject: Data modeling question
I was reading one of the papers on the quest website about data modeling.
An example was presented and I did not believe the
results so I tried it out. Of course the writer ( Phd) was correct.
Does anyone know why does not enforce RI constraint if any of the foreign
key colums are NULL. I took it literally that if I insert any
record in table_2 that a corresponding record must be in the
parent(table_1). Apparently this is not so.
Someone please explain.
Thanks
Rick
drop table table_2;
drop table table_1;
create table table_1 (
a number not null,
b number not null,
c number,
constraint table_1_pk primary key (a,b));
create table table_2 (
a number,
b number,
d number not null,
e number not null,
f number,
constraint pk_table_2 primary key (d,e),
constraint fk_table_2_reference_table_1 foreign key (a,b)
references table_1 (a,b))
/
insert into table_2 values(1,NULL,3,4,5);
1 row processed.
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