Re: Is a primary key made of a couple columns so much better than a unique() constraint ? - Mailing list pgsql-general

> Just for the sake of completeness, there are exactly two differences:
> * PRIMARY KEY implies NOT NULL on the key columns; UNIQUE doesn't.
> * PRIMARY KEY creates a default target for foreign key references,
>   ie, if you've declared a primary key then you can later just say
>   "REFERENCES mytab" instead of spelling out "REFERENCES mytab(keycol)".
> So "UNIQUE + NOT NULL" is pretty dang close to the same as "PRIMARY
> KEY", but not quite.
>             regards, tom lane

Thanks too, Tom :-)

Best regards,
David

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David Pradier -- Directeur Technique de Clarisys Informatique -- Chef de projet logiciels libres / open-source