SQL displaying multiple records - php

Question

I am currently working on a school time-table management system wherein the student dashboard, Time-table is displayed according to the current day, but when displaying the data, two duplicates come out of nowhere.
Initially, I joined the tables 'students' and 'timetable' through an 'INNER JOIN', but the problem with it was duplicates being placed simultaneously which was later fixed with 'RIGHT JOIN'.
Now, the duplicates display after the entire table has been printed.
HERE IS THE CODE BELOW:-
<?php
require_once("connection.php");
function information($subject, $time, $day, $teacher){
$element = "
<tr>
<td>$subject</td>
<td>$time</td>
<td>$day</td>
<td>$teacher</td>
</tr>
";
echo $element;
}
function getData(){
global $conn;
$sql = '
SELECT DISTINCT students.roll_no
, students.class_room
, timetable.subject_name
, timetable.time_code
, timetable.day_otw
, timetable.teacher_name
FROM students
RIGHT
JOIN timetable
ON students.class_room = timetable.room_no;
';
$result = mysqli_query($conn, $sql);
$mydate=getdate(date("U"));
if(mysqli_num_rows($result) > 0){
while($row=mysqli_fetch_assoc($result)){
if($mydate['weekday'] == $row['day_otw']){
information($row['subject_name'], $row['time_code'], $row['day_otw'], $row['teacher_name']);
}
}
} else {
echo "
<h1 class=\"check-data\">Sorry, You haven't been assigned a class yet!</h1>
<h3 class=\"ask\">Please contact your teacher/supervisor for more information.</h3>
";
}
}
getData();
?>
SO BASICALLY THE ENTIRE TABLE IS BEING DUPLICATED TWICE.

Answer 1

Outer joining makes no sense here. You neither want students without a timetable entry (LEFT OUTER JOIN), nor timetable entries without students (RIGHT OUTER JOIN). Then you are using DISTINCT because you are fightig duplicates, which is a bad idea, because thus you don't examine where the duplicates stem from. There should be no duplicates in the first place, so probably there is something wrong with the join criteria or data. You should fix this instead of looking for inappropriate workarounds.
Your join criteria is that the student is in the same room as the timetable entry. Why is the student associated a room? Do all the student's classes take place in the same room? In that case, yes, a class room would mean a class and then the tables would be related by the class (room). But if that were the case, you would get no duplicates.
I assume there to be something else to relate students with the timetable. Look for a student ID in the timetable. Something like:
SELECT s.roll_no, s.class_room, t.subject_name, t.time_code, t.day_otw, t.teacher_name
FROM students s
JOIN timetable t ON s.student_id = t.student_id
ORDER BY s.student_id, t.day_otw, t.time_code;
Or maybe there is something like an additional class ID, both student and timetable belong to? (The room in both tables would look strange then, however.) Maybe you don't know the database well enough. If this is the case, ask somebody who does.

Answer 2

From your screen, you only need to display timetable data, so there is no point to link to student table
Please consider using the following instead of your right join
SELECT
timetable.subject_name, timetable.time_code,
timetable.day_otw, timetable.teacher_name
FROM timetable