Re: Atomicity?

[Richard Broersma Jr <rabroersma(at)yahoo(dot)com>]

> Naz Gassiep <naz(at)mira(dot)net> writes:
> > I would like more information on this deficiency and what causes it so I 
> > know when to anticipate it.
> 
> The uniqueness constraint is checked on a row-by-row basis, so if you
> update one row to hold the same value as another row holds, you get an
> error immediately.  It doesn't matter that if the query had been allowed
> to finish, it would have updated that other row to some non-conflicting
> value.  (You might be able to work around this if you could control the
> order in which rows are updated, but you can't.)
> 
> This is not what the SQL spec says should happen, but so far no one has
> proposed a reimplementation that doesn't give up unreasonable amounts
> of performance.  It's on the TODO list ...
 
Is this related to the current limitations of "SET CONSTRAINTS"?
http://www.postgresql.org/docs/8.1/interactive/sql-set-constraints.html

Regards,

Richard Broersma Jr.