Re: Primary Keys

cooper_at_cimage.com (Wendy Cooper) wrote:

>[ Article crossposted from comp.databases.oracle ]
>[ Author was Steve Butler ]
>[ Posted on Wed, 19 Apr 1995 12:45:54 -0700 ]

>On 13 Apr 1995, pconnors on BIX wrote:
>> DPWCC02.OBERLE02_at_SSW.ALCOA.COM (Oberle, John F.) writes:
>> >Can someone tell me the significance of the primary key
>> >constraint. What are the advantages or disadvantages over
>> >creating unique indexes.

Although a unique index does not allow duplication of a row in the table based on that key, it quite different to a Primary Key. A primary key is a conceptual object used to enforce referential integrity. A unique index is a physical object used to enforce the PK or a Uniqueness constraint.

Without rambling on too much, basically a PK is used in conjunction with a FK to stop detail rows being inserted into the database without a corresponding master row. I think you would find if you created a unique index it would be used to enforce the PK contraint rather than creating the PK first.

Gordon
>> The primary key constraint creates a unique index, but it
>> uses a system-generated name and defaults the storage and
>> tablespace. For that reason, our shop is putting a standard
>> in place that constraints are to have the index name
>> and storage info created explicitly.
 

>Perhaps in versions prior to 7.0.16. (There was a minor problem I ran
>into in 7.0.13 having to do with EXP and IMP.)
 

>Now you can specify the storage paremeters and tablespace for the primary
>key constraint within the CREATE TABLE statement.
 

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gordonh_at_acslink.net.au
RIPLEY, Queensland, Australia Received on Wed Apr 26 1995 - 00:00:00 CEST