Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter?
| От | Glen Huang |
|---|---|
| Тема | Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter? |
| Дата | |
| Msg-id | 9AD86454-4EFE-4B77-A977-3D55F64483AA@gmail.com обсуждение исходный текст |
| Ответ на | Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter? ("David G. Johnston" <david.g.johnston@gmail.com>) |
| Ответы |
Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter?
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| Список | pgsql-general |
Thanks.
Didn't realize it could be implemented with a exclusion constraint. The comparing between any two row definitely sounds like the right direction. But I'm still having a hard time figuring out how i should write the `exclude_element WITH operator` part, which I think, should detect if specified columns consist of the same items, regardless the order? could `exclude_element` contains multiple columns? (from the syntax it looks like it's impossible) And is there such an operator to compare multiple columns?
On 23 Mar 2017, at 1:04 AM, David G. Johnston <david.g.johnston@gmail.com> wrote:Hello,
If I have a table like
CREATE TABLE relationship (
obj1 INTEGER NOT NULL REFERENCES object,
obj2 INTEGER NOT NULL REFERENCES object,
obj3 INTEGER NOT NULL REFERENCES object,
...
)
And I want to constrain that if 1,2,3 is already in the table, rows like 1,3,2 or 2,1,3 shouldn't be allowed.
Is there a general solution to this problem?
Sorry if the question is too basic, but I couldn't find the answer in the doc, at least not in the chapter on unique index.The most direct option to consider is a exclusion constraint.https://www.postgresql.org/docs/current/static/ddl-constraints.html (bottom of page)David J.
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