This is more or less correct, I was looking for performance gains on
the [possible] differences during DML and DDL.
If Jim is correct, is there a particular reason that PostgreSQL does
not behave like other RDBMs without a SET ALL DEFERRED? Or is this a
discussion best left for -HACKERS?
On 2/27/07, Jim C. Nasby <[EMAIL PROTECTED]> wrote:
On Tue, Feb 27, 2007 at 06:43:51PM -0600, John Jawed wrote:
> Is there any difference as far as when the "uniqueness" of values is
> checked in DML between a unique index vs a unique constraint? Or is
> the only difference syntax between unique indices and constraints in
> PostgreSQL?
Syntax only, AFAIK. I prefer using constraints if I actually want to
constrain the data; it makes it clear that it's a restriction.
In some databases if you know that an index just happens to be unique
you might gain some query performance by defining the index as unique,
but I don't think the PostgreSQL planner is that smart. There can also
be some additional overhead involved with a unique index (vs
non-unique), such as when two backends try and add the same key at the
same time (one of them will have to block).
--
Jim Nasby [EMAIL PROTECTED]
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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