Andrew,
> > Can someone tell me what advantage there is to creating a table
> with a
> > primary key rather than simply adding a unique index to the table
> at a
> > later time.
If you are a serious DBA, one of the important rules to follow is "Never
create any table without a Primary Key." One can achieve the same
result by adding a UNIQUE index on a NOT NULL column later, but the
danger is that you'll forget and go into production with an un-keyed
table. Believe me, I've done it, and didn't realize what was wrong
until I got a "Could not identify unique tuple" error.
For an extensive discussion of why primary keys are important, see
"Practical Issues in Database Management" (F. Pascal).
-Josh Berkus
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