Ah Bon wrote:
> I have the following database structure :
>
> my_user ( id, name );
> my_country (id, name );
> my_travel ( id_user , id_country , length_of_stay );
>
> id_user AND id_country are both external keys. They references my_user
> and my_country.
>
> In mysql, innoDB engine, is it better to :
>
> 1/ add 2 foreign key constraints to my_travel.id_user and
> my_travevl.id_country
>
> or
>
> 2/ add only one unique key on (id_user, id_country)
>
> The basic fact is : when I add foreign key constraints AND unique key,
> mysql tells me that my_travel fields should'nt be part of an unique and
> foregn key in the same time.
>
> Any ideas ?

I wouldn't think you would want a unique key on id_user and id_country.
For instance - what happens if a user makes multiple trips to the
same country? Wouldn't you want to be able to list all the trips?


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Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
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