Question

I’m working on an application which has different types of users i.e. students, tutors, and administrators. However, I initially set up my database to have only two tables: Users (that holds all the login information, common to all types) and Profiles (that holds all other information; though each column applies to a certain type of user).

I was thinking maybe I should have Users, and 3 separate tables for each type i.e. Students, Tutors, and Administrators. However, how do I link those three tables with Users table? I’m sure there would be a bridge table but I’m not too sure how to do that.

Answer 1

This should be a solid starting point for you. Define the tables which it sounds like you are ok with, then apply the relationships using the ALTER TABLE command. See below.

CREATE TABLE Users
(
ID INT IDENTITY (1,1),
PRIMARY KEY (ID),
UserName VARCHAR(20),
Password VARCHAR(20)
)

CREATE TABLE Students
(
ID INT IDENTITY (1,1),
PRIMARY KEY (ID),
UserID INT --foreign key to Users.ID column
--Other columns
)

CREATE TABLE Tutors
(
ID INT IDENTITY (1,1),
PRIMARY KEY (ID),
UserID INT --foreign key to Users.ID column
--Other columns
)

CREATE TABLE Administrators
(
ID INT IDENTITY (1,1),
PRIMARY KEY (ID),
UserID INT --foreign key to Users.ID column
--Other columns
)
--Apply foreign key relationships
ALTER TABLE Students
ADD FOREIGN KEY (UserID)
REFERENCES Users(ID)

ALTER TABLE Tutors
ADD FOREIGN KEY (UserID)
REFERENCES Users(ID)

ALTER TABLE Administrators
ADD FOREIGN KEY (UserID)
REFERENCES Users(ID)