Re: multiple UNIQUE indices for FK

W dniu 28.02.2016 o 03:35, David G. Johnston pisze:
> W dniu 23.02.2016 o 09:39, Rafal Pietrak pisze:
> > Can anybody suggest any other way out of this mass?
>
>
> ​The only thought that sticks while reading your prose is:​
>
> ​message ----> message-person <---- person​
>
>
> ​message-person (message_id, person_id, relationship_type[sender,
> receiver])

It just occured to me: how do I make sure (e.g. force within a database) with the above structure, that a message can have *only one* sender?
but, allow for multiple recepients?

-R

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If I'm not too late, unique partial index:

CREATE UNIQUE INDEX unique_message_sender (message_id, person_id) WHERE relationship_type = sender;

Regards,
Igor