Re: How would i do this? - Mailing list pgsql-general

I'd call this student-cross-class table "enrollments" as it
records when a student enrolls in a class.  You may want a
trigger on insert on it.  For example if the sudent is already
enrolled in the same class or another class the meets at an over
lapping time.  One thing I whished for when going to school
at a large university was a check that back to back classes
where within close enough distance so you would not always be
late to the second class.  I think I had 10 minutes to walk
over a mile once.


--- wsheldah@lexmark.com wrote:
>
>
> That works fine right up until the student wants to sign up for her
> second
> class. There needs to be an intersection table that just stores
> class-student
> combinations:
>
> create table class-student (id serial primary key, student_id
> integer, class_id
> integer);
>
> with appropriate indexes. Then each student can take as many classes
> as they
> like, a class can have as many students enrolled as the school
> allows, but you
> don't waste space if they take fewer classes or have a low
> enrollment. And it
> stays normalized. Etc. But like the others said, there's lots of
> literature
> about this, most of it starting with the teacher-class-student
> situation, so
> you're in luck.  :-)
>
> Wes Sheldahl
>
>
>
>
> Vince Vielhaber <vev%michvhf.com@interlock.lexmark.com> on 12/11/2001
> 03:26:09
> PM
>
> To:   John Hughes <johughes%shaw.ca@interlock.lexmark.com>
> cc:   pgsql-general%postgresql.org@interlock.lexmark.com (bcc: Wesley
>       Sheldahl/Lex/Lexmark)
> Subject:  Re: [GENERAL] How would i do this?
>
>
> On Tue, 11 Dec 2001, John Hughes wrote:
>
> > I am new to DB programming, so im not too sure about how to
> implement my DB.
> >
> > Here is what i need: a DB with tables of:
> >
> > 1. Students.
> > 2. Classes
> > 3. Teachers
> > 4. Assignments
> >
> > Each teacher can be assigned a class, which is compromised of a
> list of
> > students. Each class can be given assignments.
> >
> > Coming from a programming background, I could do this in c++ very
> easily. I
> > actually started inmplementing it in a similar fasion: each student
> class
> > teacher ect would have a uniqe id in the database, and, for
> example, a
> > class would include an array of integer student id's.
> >
> > This seems really error prone, and not very efficient.
> >
> > what is a better implementation?
>
> Don't think array.  Look at it from the other direction.
>
> Each class has a name (prog101) a room#, teacherid, etc.  and a class
> id.
> Each student has a name, etc. and the id of the class they're taking.
>
> Then:  select name from student where classid = 4;
>
> Where 4 could be the id for prog101.
>
> That's the REALLY simplified version, but you get the idea.
>
>
> Vince.
> --
>
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=====
Chris Albertson
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