How to implement a flexible table - database

Question

I am a novice database user (not designer). I would like to implement the following item in the postgres database.
I would like to implement a database which contain the following information
Table1
Classroom | Classroom Type | AV System | Student1 | Student2 | ... | Student36
1A | 'Square' | 1 | 'Anson' | 'Antonie'| ... | 'Zalda'
1B | 'Rectangle' | 2 | 'Allen' | 'Andy' | ... | 'Zeth'
There is another table to store the seating plan for each student, that's why I created another table
Table2
Classroom Type | Student1 Position | Student2 Position | ... | Student36 Position
'Square' | (1,1) | (1,2) | ... | (6,6)
'Rectangle' | (1,1) | (1,2) | ... | (4,9)
Table3
AV System | TV | Number of Speaker
1 | 'LCD' | 2
2 | 'Projector' | 4
The reason of this implementation is to draw a seating plan. However I don't think this is a good implementation. Therefore I would like to find another way which will give me some flexibility when I want to scale it up.
Thanks in advance.

Answer 1

This is not how relational databases work. In a relational database you don't repeat attributes, you create 1:N relationships. This process is called normalization and one of its main goals is to prevent duplication of data.
As far as I can tell, the following structure would do what you want:
-- a table to store all possible classroom types ("Square", "Rectangle", ...)
create table classroom_type
(
type_id integer not null primary key,
type_name varchar(20) not null,
unique (type_name)
);
-- a table to store all classrooms
create table classroom
(
room_id integer not null primary key,
room_name varchar(5) not null,
room_type integer not null references classroom_type,
unique (room_name)
);
-- a table containing all students
create table student
(
student_id integer not null primary key,
student_name varchar(100) not null
--- ... possibly more attributes like date of birth and others ....
);
-- this table stores the combinations which student has which position in which classroom
create table seating_plan
(
student_id integer not null references student,
room_id integer not null references room,
position varchar(10) not null,
primary key (student_id, room_id), -- make sure the same student is seated only once in a room
unique (room_id, position) -- make sure each position is only used once insid a room
);
I used integer for the ID columns, but most probably you might want to use serial to automatically create unique values for them.
Most probably the model needs to be extended to include a school year as well. Because student Allen might be in room 1A this year, but in 3C next year. This would be another attribute of the seat_plan table (and would be part of the primary key)

Answer 2

|ClassRoomTypes| | ClassRooms | | TableTypes | | Tables |
|--------------| |----------------| |----------------| |------------|
|Id |<--- |Id | |Id |<- |Id |
|Name | | |Name | |Name | |--|TableType_Id|
|--------------| ---|ClassRoomType_Id| |Size_X | |------------|
|Size_Y |
|----------------|
|ClassRoomToTables| |ClassRoomToTable_Students| | Students |
|-----------------| |-------------------------| |-------------------|
|Id |<--- |Id | |Id |
|ClassRoom_Id | |--|ClassRoomToTable_Id | OR |Name |
|Table_Id | |Student_Id | |ClassRoomToTable_Id|
|-----------------| |-------------------------| |-------------------|
Now a explaination:
A Class Room has a list of tables.
A Table has some paramenters ( eg: Student Capacity; Size_X, Size_Y etc)
A Table also it's a concept, (It's not something unique identificated, a table concept is used in many class rooms)
One or many students sit at many tables in different class rooms (ClassRoomToTable_Students table)
OR
One or many students may sit only at a table from specific class room (ClassRoomToTable_Id from Students)
You may get some inspiration from my point of view, I do not guarantee that totally fits your domain case. Success