Re: Primary Keys

In article <3ob237$foq_at_inforamp.net>, <flemir_at_tdbank.ca> wrote:
>In comp.databases.oracle gordonh_at_acslink.net.au (Gordon Hooker) said:
>
>>
>>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.
>>
>I am getting confused between the merits of primary keys and unique index.
>In an Oracle course I took, the instructor recommended using primary keys
>rather than unique indexes and the Oracle7 Server Administrator's Guide
>says "it is better to create constraints to enforce uniqueness than it is
>to use the CREATE UNIQUE INDEX syntax". Somewhere else implied that CREATE
>UNIQUE INDEX was an obsolete term. However, other people seem to recommend
>using UNIQUE INDEX.

 (lines deleted)
>What looks to be the better approach - DEFINE PRIMARY KEY or
>CREATE UNIQUE INDEXES.
The way I understand it, the only difference between Primary Keys and Unique constraints is that a Unique constraints allows NULL values and PK doesn't. Both use indexes, both can be the parent of a Foreign Key relationship, and both are limited to 16 fields for composite indexes.

Vince

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