Re: DB Design Principles for RDBMS
Date: Fri, 14 Mar 2003 10:59:31 -0800
Message-ID: <3E722693.A47_at_assist.org>
Richard Wheeldon wrote:
> Help! I'm confused. How can you have a 5NF schema with derived
> data?
How about this:
create table student (
student_id int not null primary key,
last_name varchar(30) not null,
first_name varchar(30) not null,
units_completed int not null
)
Where units_completed is derived from the transcript table:
create table transcript (
student_id int not null,
course_id int not null,
term_taken char(4) not null,
units_attempted int not null,
units_completed int not null,
primary key (student_id, course_id, term_taken), foreign key (tudent_id) references student (student_id), foreign key (course_id) references course (course_id), foreign key (term_taken) references term (term_name))
student.units_completed is the sum of all transcript.units_completed for that student_id. Where is this not normalized?
Larry Coon
University of California
larry_at_assist.org
and lmcoon_at_home.com
Received on Fri Mar 14 2003 - 19:59:31 CET