Re: "RETURNING PRIMARY KEY" syntax extension - Mailing list pgsql-hackers

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.

There's generally also the restriction that for some contexts - like
e.g. foreign keys - primary/candidate keys may not be deferrable..

Greetings,

Andres Freund

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