Re: Restrictions for a specific situation in my DB
| От | JORGE MALDONADO |
|---|---|
| Тема | Re: Restrictions for a specific situation in my DB |
| Дата | |
| Msg-id | CAAY=A79H2-1vxGVbacnP7mex-WPzjoycEE-fNuGbMmi2w8tKLw@mail.gmail.com обсуждение исходный текст |
| Ответ на | Restrictions for a specific situation in my DB (JORGE MALDONADO <jorgemal1960@gmail.com>) |
| Ответы |
Re: Restrictions for a specific situation in my DB
|
| Список | pgsql-novice |
"You should always CC the list."
I am sorry for that. I will take it into consideration from now on.
so I cannot answer that."
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.
With respect,
Jorge Maldonado
On Tue, May 12, 2020 at 10:46 PM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
On Tue, 2020-05-12 at 18:27 -0500, JORGE MALDONADO wrote:
You should always CC the list.
> Does it has to be a UNIQUE INDEX?
If you want to avoid duplicates, yes.
> What about a RESTRICTION? I understand it also creates a UNIQUE INDEX behind the scenes.
> Is a RESTRICTION not supported because of the LEAST and GREATEST expressions?
> If it is, what is a reason to use a UNIQUE INDEX instead of a RESTRICTION?
> I just want to fully understand the concept.
I have never heard of a "restriction" as a technical concept in databases,
so I cannot answer that.
Yours,
Laurenz Albe
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