Re: "RETURNING PRIMARY KEY" syntax extension

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?

> 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?
-- 
Vik