Question about Primary Key

I want to create a Primay Key
as combination of 3 fields.
Prod_NO
Prod_Item
Prod_cont
In this case there is a chance that PRod_item
or Prod_Cont will be blank, can I still create
these three as Primary Key? If not, what is the
alternate way to do so?
Thank you,I would recommend having as a primary key a value that is guaranteed to be
unique in all instances for each record like the identity key, you can
certainly use your combination of fields as a 'candidate' key and compine
them in joins and such.
Troy
"Me" <Me@.discussions.microsoft.com> wrote in message
news:E7E2961B-5A43-4246-8B27-68F99477D8FA@.microsoft.com...
>I want to create a Primay Key
> as combination of 3 fields.
> Prod_NO
> Prod_Item
> Prod_cont
> In this case there is a chance that PRod_item
> or Prod_Cont will be blank, can I still create
> these three as Primary Key? If not, what is the
> alternate way to do so?
> Thank you,
>|||PK columns cannot be null. But you can get uniqueness by
creating it as a unique constraint or unique index... Bruce
>--Original Message--
>I want to create a Primay Key
>as combination of 3 fields.
>Prod_NO
>Prod_Item
>Prod_cont
>In this case there is a chance that PRod_item
>or Prod_Cont will be blank, can I still create
>these three as Primary Key? If not, what is the
>alternate way to do so?
>Thank you,
>.
>|||Bruce,
I think what you suggested will work, but do you foresee
any other problems in this? Will everything else
work the same? I haven't used it any times hence
the question.
Thank you,
-M
"Bruce de Freitas" wrote:
> PK columns cannot be null. But you can get uniqueness by
> creating it as a unique constraint or unique index... Bruce
>
> >--Original Message--
> >I want to create a Primay Key
> >as combination of 3 fields.
> >Prod_NO
> >Prod_Item
> >Prod_cont
> >
> >In this case there is a chance that PRod_item
> >or Prod_Cont will be blank, can I still create
> >these three as Primary Key? If not, what is the
> >alternate way to do so?
> >
> >Thank you,
> >
> >.
> >
>|||It depends...
PK Constraints do not allow NULLs, but UNIQUE constraints allow a single
NULL.
So if your data looked like:
1, NULL, NULL
That would be okay for a UNIQUE Constraint.
Another record of
1, NULL, NULL will violate the constraint however.
HTH
Rick Sawtell
MCT, MCSD, MCDBA
"Me" <Me@.discussions.microsoft.com> wrote in message
news:33CCE845-1F74-4FE3-9570-B79E0D442C20@.microsoft.com...
> Bruce,
> I think what you suggested will work, but do you foresee
> any other problems in this? Will everything else
> work the same? I haven't used it any times hence
> the question.
> Thank you,
> -M
> "Bruce de Freitas" wrote:
> > PK columns cannot be null. But you can get uniqueness by
> > creating it as a unique constraint or unique index... Bruce
> >
> >
> > >--Original Message--
> > >I want to create a Primay Key
> > >as combination of 3 fields.
> > >Prod_NO
> > >Prod_Item
> > >Prod_cont
> > >
> > >In this case there is a chance that PRod_item
> > >or Prod_Cont will be blank, can I still create
> > >these three as Primary Key? If not, what is the
> > >alternate way to do so?
> > >
> > >Thank you,
> > >
> > >.
> > >
> >