Re: data definition

"Gavin Sim" <schowe_at_singnet.com.sg> writes:

> Hi Tim,
> thanks for your comment. This is only part of my modelling being reviewed.
> Actually i am trying to practise on the data definition on oracle thus my
> data model isn't that important at this point of time. But i did realised
> there is mistake and made the necessary amendments.
>
> Given the sample below the info_no is the primary key of the hotel.
> hotel_no and room_no are the primary keys
>
> information(info_no, hotel_no, room_no, datetime)
> hotel(hotel_no, hotel_name, Hotel_district)
> room(room_no, room_describe)
>
>
> Given the information above, how can I write in data definition in a way
> that i can ensure (no hotel or room can have 2 different information at the
> same time. This mean a user can only register in a hotel or register a room
> at the same time and not register 2 rooms or 2 hotels at the same time.
>
> can I use constraint check( unique(hotel,room)...... on the information
> table?
> I know this is wrong too sign.

Well....

I think your data model still lacks the necessary information to achieve what you want. If you make hotel_no and room_no unique, then you will only ever be able to have one record for each combination.

Tim

-- 
Tim Cross
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