SQL tables with boolean variables - sql

Question

I am kind of new to SQL using and i am playing with different scenarios.
My Example is as follows :
Suppose that i need to have a student enrollment system . I created the student table as follows :
create table student (net_id char(10) , first_name char(20) ,
last_name char(20) , Major char(10) , ISGraduate BOOLEAN,
primary key (net_id)
where isgraduate boolean variable measures whether a student is a graduate student or not.
I have a another entity which is professor as follows :
create table professor (net_id char(10) , first_name char(20)
, last_name char(20) , Rank char(10) , department char(20) ,
primary key (net_id))
Then if i want to model the relationship : a professor can advise many graduate students , then i might need to create a new table adviosry , But in there how can i filter only the graduate students ?
any help would be great .
Thank you.

Answer 1

You can create the table advisory like this:
create table advisory (
professor_id char(10),
student_id char(10),
ISGraduate BOOLEAN default 1,
foreign key (professor_id) references professor(net_id),
foreign key (student_id, ISGraduate) references student(net_id, ISGraduate),
primary key (professor_id, student_id)
);
and add a unique index in the table student for the columns net_id and ISGraduate:
create table student (
net_id char(10),
first_name char(20),
last_name char(20),
Major char(10),
ISGraduate BOOLEAN,
unique(net_id, ISGraduate),
primary key (net_id)
);
See the demo.
Also make sure that the flag foreign_keys is ON by executing:
PRAGMA foreign_keys = ON;
and get the graduate students from this table with a join to student:
select s.*
from student s inner join advisory a
on s.net_id = a.student_id