On 08/03/2012 12:07 PM, Chris Angelico wrote:
On Fri, Aug 3, 2012 at 10:00 AM, Craig Ringer <ringerc@xxxxxxxxxxxxx> wrote:
-- PostgreSQL specific hack you can use to make
-- really sure only one row ever exists
CREATE UNIQUE INDEX there_can_be_only_one
ON invoice_number( (1) );
This will guarantee that there's only one row. Does Postgres then
optimize anything based on this? I have a couple of cases where I'm
using a table to store global configuration, and selecting/updating
that table without a WHERE clause to manipulate it. Can PostgreSQL
notice the "highlander" status of the table and know not to go looking
for more?
As far as I know, no. If anything it could slow things down a tad. I
just like to be really sure it's a single row table.
An `ON INSERT OR DELETE` trigger that throws is probably a more sensible
option, really.
--
Craig Ringer
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