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To: pgsql-sql@postgresql.org
Subject: Re: Unique index VS unique constraint
Date: Fri, 04 Oct 2013 19:41:17 +0200
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Il 04/10/2013 18:48, JORGE MALDONADO ha scritto:
> I have search for information about the difference between "unique
> index" and "unique constraint" in PostgreSQL without getting to a
> specific answer, so I kindly ask for an explanation that helps me
> clarify such concept.
2 main differences.
First is the meaning: primary key identifies a record. A unique just
tells you that that value of the record, in the table is unique. If you
use keys, db structure will be more intelligible (my opinion).
Second one is functional: in an unique constraint you can allow NULL
values and ignore them. A primary key does not allow this.
> Respectfully,
> Jorge Maldonado
Regards,
Luca.
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Subject: Re: Unique index VS unique constraint
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