php/mysql how to join three tables - php

Question

I'm writing code for a school transcript system. However, I'm stuck in joining the tables which are the courses table I named 'causes', courses registered table I named 'courses_registered' and the students table 'students' actually the join works, but the problem is that data are repeated in multiples depending on how many data rows that are on the courses_registered table for example, if have 2 courses registered, I get 4 rows echoed out from all tables instead of two. so my question is, how can i join these three tables perfectly without data being repeated, when i loop through the data. this is the table structure for the three tables.
--
-- Table structure for table `courses`
--
CREATE TABLE IF NOT EXISTS `courses` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`course_code` varchar(255) NOT NULL,
`course_title` varchar(255) NOT NULL,
`cl` int(255) NOT NULL,
`level` int(255) NOT NULL,
`session` varchar(255) NOT NULL,
`semester` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;
--
-- Dumping data for table `courses`
--
INSERT INTO `courses` (`id`, `course_code`, `course_title`, `cl`, `level`, `session`, `semester`) VALUES
(1, 'GSS 111', 'Use of English', 3, 1, '2009/2010', '1'),
(2, 'GSS 112', 'Nigerian History', 2, 1, '2009/2010', '1');
--
-- Table structure for table `courses_registered`
--
CREATE TABLE IF NOT EXISTS `courses_registered` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`course_id` int(255) NOT NULL,
`student_id` int(255) NOT NULL,
`score` int(255) NOT NULL,
`grade` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;
--
-- Dumping data for table `courses_registered`
--
INSERT INTO `courses_registered` (`id`, `course_id`, `student_id`, `score`, `grade`) VALUES
(1, 1, 2, 60, 'B'),
(2, 2, 2, 80, 'A');
-- --------------------------------------------------------
--
-- Table structure for table `students`
--
CREATE TABLE IF NOT EXISTS `students` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`regno` varchar(255) NOT NULL,
`college` varchar(255) NOT NULL,
`dept` varchar(255) NOT NULL,
`level` varchar(255) NOT NULL,
`fname` varchar(255) NOT NULL,
`lname` varchar(255) NOT NULL,
`no_of_semesters` int(255) NOT NULL,
`gender` varchar(255) NOT NULL,
`dob` varchar(255) NOT NULL,
`age` int(255) NOT NULL,
`mstatus` varchar(255) NOT NULL,
`nationality` varchar(255) NOT NULL,
`religion` varchar(255) NOT NULL,
`address` varchar(255) NOT NULL,
`email` varchar(255) NOT NULL,
`phone` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;
--
-- Dumping data for table `students`
--
INSERT INTO `students` (`id`, `regno`, `college`, `dept`, `level`,
`fname`, `lname`, `no_of_semesters`, `gender`, `dob`, `age`,
`mstatus`, `nationality`, `religion`, `address`, `email`, `phone`)
VALUES
(2, 'MOUAU 09/14508', 'CEET', 'Electrical Electronics Engineering',
'1', 'Nnamdi', 'Okoro', 2, 'Male', '24-07-1989', 25, 'Single',
'Nigerian', 'christian', 'Okpu Umiobo road, Aba',
'nokoro#gmail.com', '09056733333');
Then this is the query
<?php
$sql = "
SELECT c.id as course_id
, c.course_code
, c.course_title
, c.cl
, c.level
, c.session
, c.semester
, r.id as rid
, r.course_id
, r.student_id
, r.score
, r.grade
, s.id
, s.regno
, s.fname
, s.lname
, s.no_of_semesters
FROM courses_registered r
JOIN courses c
ON r.course_id = course_id
JOIN students s
ON s.id = r.student_id
WHERE s.id = '$id'
";
$result = mysqli_query($con,$sql) or die ('Could not show students records.'. mysqli_error($con) );
if (mysqli_num_rows($result) > 0 ){
//echo mysqli_num_rows($result);
while($row = mysqli_fetch_array($result) ){
$score[] = $row['score'];
$course_code[] = $row['course_code'];
$course_title[] = $row['course_title'];
$cl[] = $row['cl'];
$grade[] = $row['grade'];
}

Answer 1

Try change this
ON r.course_id = course_id
to
ON r.course_id = c.id