On 2014-06-11 00:21:58 +0200, Vik Fearing wrote:
> On 06/09/2014 07:13 PM, Andres Freund wrote:
> > On 2014-06-09 13:42:22 +0200, Vik Fearing wrote:
> >> On 06/09/2014 09:06 AM, Gavin Flower wrote:
> >>> From memory all unique keys can be considered 'candidate primary keys',
> >>> but only one can be designated 'the PRIMARY KEY'.
> >>
> >> Almost. Candidate keys are also NOT NULL.
> >
> > The list actually is a bit longer. They also cannot be partial.
>
> What? AFAIK, that only applies to an index. How can the data itself be
> partial?
I don't follow? Gavin above talked about unique keys - which in postgres
you can create using CREATE UNIQUE INDEX. And if you make those partial
they can't be used for this purpose.
> > There's generally also the restriction that for some contexts - like
> > e.g. foreign keys - primary/candidate keys may not be deferrable..
>
> Again, what is deferrable data?
You can define primary/unique constraints to be deferrable. c.f. CREATE
TABLE docs.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services
