Grading system using php and mysql - php

Question

In the database, some courses value are NULL, and I don't want to print courses that hava a NULL value.
I don't know how I can achieve this in php or mysql. I need something like so:
if(course1!=NULL || course2!=NULL || course3!=NULL || course4!=NULL){
// echo course1; echo course2; echo course3; echo course4; }
The database looks like this:
And the output so far look like this:
A remark() function which check whether the course is A, B, C, D, E, or F is not working properly.
I want the remark() function to output either Excellent, Credit, Pass, or fail base on the grade.
Follows is the code:
function remark(){
global $mathematics, $physics, $chemistry, $lang;
if($mathematics=='A' || $physics=='A' || $chemistry=='A' || $lang=='A'){
$remark = "Excellent";
}
elseif($mathematics=='B' || $physics=='B' || $chemistry=='B' || $lang=='B' || $mathematics=='C' || $physics=='C' || $chemistry=='C' || $lang=='C'){
$remark = "Credit";
}
elseif($mathematics=='D' || $physics=='D' || $chemistry=='D' || $lang=='D' || $mathematics=='E' || $physics=='E' || $chemistry=='E' || $lang=='E'){
$remark = "Pass";
}
else{
$remark = "Fail";
}
return $remark;
}
if(isset($_POST['student_id']) && !empty($_POST['student_id'])){$student_id = $_POST['student_id'];
$check = "SELECT * FROM sample1 WHERE student_id='$student_id'";
$check_query = mysqli_query($connection, $check);
if(mysqli_num_rows($check_query)>0){
while($query_row = mysqli_fetch_assoc($check_query)){
$mathematics = $query_row['mathematics'];
$physics = $query_row['physics'];
$chemistry = $query_row['chm'];
$lang = $query_row['lang'];
echo "<table border=1 width=50%>
<tr> <td>Name: ".$query_row['name']." </td>
<td>Student Id: ".$query_row['student_id']."</td>
<td>Level: ".$query_row['level']."</td>
</tr>
<tr>
<th> Course </th>
<th> Grade </th>
<th> Remark </th>
</tr>
<tr> <td>Mathematics </td> <td>".$mathematics." </td></td> <td>".remark()." </td></tr>
<tr> <td>Physics </td> <td>".$physics."</td> </td><td>".remark()." </td></tr>
<tr> <td>Chemistry </td> <td>".$chemistry."</td> </td><td>".remark()." </td></tr>
<tr> <td>Language </td> <td>".$lang."</td> </td><td>".remark()." </td></tr>
</table>";
}
}
else{echo "Record not found";}
}

Answer 1

About the MYSQL not null values, you use this:
SELECT * FROM yourtable WHERE course1 IS NOT NULL
So, IS NOT NULL will give you queries where that column (course1) is not null. Here more info.
And for PHP, your remark() function has a wrong approach. I will give you one that is correct for your purpouse.
function remark($course){
switch($course) {
case 'A':
return 'Excellent';
break;
case 'B':
case 'C':
return 'Credit';
break;
case 'D':
case 'E':
return 'Pass';
break;
default:
return 'Fail';
break;
}
}
So in your HTML table you do this for each course:
while ($query_row = mysqli_fetch_assoc($check_query)) {
$mathematics = $query_row['mathematics'];
$physics = $query_row['physics'];
$chemistry = $query_row['chm'];
$lang = $query_row['lang'];
echo "<table border=1 width=50%>
<tr> <td>Name: " . $query_row['name'] . " </td>
<td>Student Id: " . $query_row['student_id'] . "</td>
<td>Level: " . $query_row['level'] . "</td>
</tr>
<tr>
<th> Course </th>
<th> Grade </th>
<th> Remark </th>
</tr>"
if(!is_null($mathematics)) echo "<tr> <td>Mathematics </td> <td>" . $mathematics . " </td></td> <td>" . remark($mathematics) . " </td></tr>";
if(!is_null($physics)) echo "<tr> <td>Physics </td> <td>" . $physics . "</td> </td><td>" . remark($physics) . " </td></tr>";
if(!is_null($chemistry)) echo "<tr> <td>Chemistry </td> <td>" . $chemistry . "</td> </td><td>" . remark($chemistry) . " </td></tr>";
if(!is_null($lang)) echo "<tr> <td>Language </td> <td>" . $lang . "</td> </td><td>" . remark($lang) . " </td></tr>";
echo "</table>";
}

Answer 2

Quick answer for the first issue extending the answer of #P0IT10n (?):
<?php
if(!is_null($mathematics)) {
?>
<tr> <td>Mathematics </td> <td>".$mathematics." </td></td> <td>".remark($mathematics)." </td></tr>
<?php
}
?>
// repeat for other courses
BUT
rethink your database structure.
Once you have another course you're f***...
Courses should have their own table, results another one.
Read about database normalisation!
EDIT
Another extension:
It would be even easier if you'd have an array like this:
$remarks = array('A'=>'Excellent', 'B'=>'Good',...);
then you need no extra function with a switch, all you need to do is:
echo $remarks[$mathematics]; // -> Excellent