Postgres Pro
Downloads
Home   >   mailing lists

Thread: Problems defining a primary key !!

Problems defining a primary key !!

From
Nagib Abi Fadel
Date:
Hi ,
i'm doing the planification of the courses in a university.
I have definned the following tables:
 
1- Table DAY representing a day (day_id,year,month ...)
2- Table PERIODE representing an hour of a day (periode_id,starting,ending,periode_number)
3- Table TEACHER representing a teacher (teacher_id,name,phone,address ...)
4- Table ROOM representing a ROOM in the university (room_id,description,name ...)
5- Table COURSE representing a course given by a teacher (course_id,name,...)
 
Now i have to planify the courses:
So i created the
following table PLANIFY(day_id,periode_id,teacher_id,room_id,course_id)
 
THE PROBLEM IS THAT I DON'T HAVE A WAY TO DEFINE A PRIMARY KEY for the table PLANIFY.
We must note that: 
1- a teacher can not give 2 courses in the same peiode on the same day, and can not exist in 2 different rooms in the same periode on the same day.
2- a room can not be occupied by 2 courses or 2 teachers in the same periode on the same day.
3- a course can not be given by 2 teachers or in 2 different rooms
 
ANY IDEAS ??
 
SHOULD I CHANGE THE STRUCTURE OF THE TABLE OR DEFINE A TRIGGER (which i don't know how to by the way).
 
thx for any help.
 
 
 
 
 
 

Do you Yahoo!?
The New Yahoo! Shopping - with improved product search

Re: Problems defining a primary key !!

From
Karsten Hilbert
Date:
> 1- Table DAY representing a day (day_id,year,month ...)
> 2- Table PERIODE representing an hour of a day (periode_id,starting,ending,periode_number)
> 3- Table TEACHER representing a teacher (teacher_id,name,phone,address ...)
> 4- Table ROOM representing a ROOM in the university (room_id,description,name ...)
> 5- Table COURSE representing a course given by a teacher (course_id,name,...)
>
> following table PLANIFY(day_id,periode_id,teacher_id,room_id,course_id)
>
> THE PROBLEM IS THAT I DON'T HAVE A WAY TO DEFINE A PRIMARY KEY for the table PLANIFY.
You can always define your own primary key with the SERIAL
datatype.

> We must note that:
> 1- a teacher can not give 2 courses in the same peiode on the same day, and can not exist in 2 different rooms in the
sameperiode on the same day. 
unique (periode_id, day_id, teacher_id, course_id)
unique (periode_id, day_id, teacher_id, room_id)

> 2- a room can not be occupied by 2 courses or 2 teachers in the same periode on the same day.
unique (periode_id, day_id, room_id, course_id)
unique (periode_id, day_id, room_id, teacher_id) (redundant, see above)

> 3- a course can not be given by 2 teachers or in 2 different rooms
unique (course_id, teacher_id)
unique (course_id, room_id)

Does that help ?

Karsten
--
GPG key ID E4071346 @ wwwkeys.pgp.net
E167 67FD A291 2BEA 73BD  4537 78B9 A9F9 E407 1346

Re: Problems defining a primary key !!

From
Richard Huxton
Date:
On Tuesday 07 October 2003 11:38, Nagib Abi Fadel wrote:
> Hi ,
> i'm doing the planification of the courses in a university.
> I have definned the following tables:
>
> 1- Table DAY representing a day (day_id,year,month ...)
> 2- Table PERIODE representing an hour of a day
> (periode_id,starting,ending,periode_number) 3- Table TEACHER representing a
> teacher (teacher_id,name,phone,address ...) 4- Table ROOM representing a
> ROOM in the university (room_id,description,name ...) 5- Table COURSE
> representing a course given by a teacher (course_id,name,...)
>
> Now i have to planify the courses:
> So i created the
> following table PLANIFY(day_id,periode_id,teacher_id,room_id,course_id)
>
> THE PROBLEM IS THAT I DON'T HAVE A WAY TO DEFINE A PRIMARY KEY for the
> table PLANIFY. We must note that:

You do (day,period,teacher), but you'll need UNIQUE constraints on
day,period,room and day,period,course too.

Alternatively, two tables (*=primary key)

t1 (day*, period*, teacher*, course)
t2 (day*, period*, course*, room)

You could pick different combinations of p,t,c depending on your model.
--
  Richard Huxton
  Archonet Ltd