How to organize common columns to a single table? - database

Question

I'm very new to database designing and I'm creating a small project to understand it better, I'm trying to come up with a new school crm. I started with the below schema:
create table student(
id int not null,
firstname varchar(100),
lastname varchar(100),
PRIMARY key (id)
);
create table address(
id int not null,
street varchar(30) not null,
city varchar(30) not null,
PRIMARY KEY (id)
);
-- they have own roles for app
create table guardians(
id int not null,
firstname varchar(100),
lastname varchar(100),
primary key (id)
);
-- teacher have own roles
create table teacher(
id int not null,
firstname varchar(100),
lastname varchar(100),
PRIMARY key (id)
)
guardians and teachers will have password for login the web portal. The reason why I created separate table is mainly because teachers might have column's like salary, schoolId etc in the future. But now if I look at the schema here, mostly the firstName, lastname is common for all student, teacher and guardians.
How can I have a common table for such repeatable field names? Or this design is good? Also I wanted to have another table ROLE which going to give permissions at app level to update/insert certain tables. Not sure how can I design it as well.

Answer 1

The schema you have planned will end up having and lot of redundancies in different tables (like firstName and lastName as you have described for each of the three tables). Also, if in future a new role turns up you will be creating new table and leading to more redundancy.
I would suggest it would we better if you create one table for user and define role of the user in that table.
e.g.:
create table user(
u_id int not null,
firstname varchar(100),
lastname varchar(100),
role varchar(100),
PRIMARY key (id)
);
You can maintain role specific data in different table and can be accessed via primary key of user table.
e.g.:
create table teacher(
t_id int not null,
u_id int,
Salary int,
qualification varchar(100),
PRIMARY key (id),
FOREIGN KEY (u_id) REFERENCES user(u_id)
)
Having a role column in user table will solve your second problem as well.