Re: Constraints, anyone?

James,

Primarily because the constraint term comes from the SQL world. In
fact, if you defined a table using SQL DDL and give it a primary key
constraint, you'll get what looks like a regular uniquely keyed
physical *FILE object on the i.

There is one difference, a DDS uniquely keyed physical file or a file
with a unique key constraint allows NULLable fields as part of the
key. So you could have multiple records with the same NULL key value.

Whereas fields that are part of a primary key constraint must also be
defined NOT NULL.

HTH,
Charles


On Mon, Dec 14, 2009 at 4:22 PM, James H. H. Lampert
<jamesl@xxxxxxxxxxxxxxxxx> wrote:

Tommy.Holden@xxxxxxxxxxxxxxxxxxxxx wrote:

primary key = unique keyed PF

So why is it available as a constraint, as opposed to simply creating
the PF as keyed? And conversely, assuming the PF is already keyed, is it
necessary to add a primary key constraint to the file in order to use it
in referential constraints?

--
JHHL
--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/midrange-l.