| From: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
|---|---|
| To: | JORGE MALDONADO <jorgemal1960(at)gmail(dot)com>, pgsql-novice <pgsql-novice(at)postgresql(dot)org> |
| Subject: | Re: Restrictions for a specific situation in my DB |
| Date: | 2020-05-13 20:26:53 |
| Message-ID: | 9a0d712598b38a190c81da043b5e9620d54a96b3.camel@cybertec.at |
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| Lists: | pgsql-novice |
On Wed, 2020-05-13 at 09:10 -0500, JORGE MALDONADO wrote:
> What I meant was "CONSTRAINT". I understand that, in PostgreSQL, I can define "UNIQUE INDEX"
> and "UNIQUE CONSTRAINT" and that a "UNIQUE CONSTRAINT" creates a "UNIQUE INDEX" behind the scenes.
>
> So my question is:
> Can a "UNIQUE CONSTRAINT" be used instead of a "UNIQUE INDEX"?
>
> I searched the web for an answer and found that expressions like LEAST and GREATEST are
> not allowed in a UNIQUE CONSTRAINT but they can be used in a UNIQUE INDEX. I also tested
> directly in a table and I could verify it. So, a UNIQUE INDEX is the choice to include
> LEAST and GREATEST.
You got it.
A unique constraint can only be defined on columns, not on expressions.
But unique indexes can have an expression as key.
Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com
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