Making links with PHP

[kows]

you have this query:

SELECT Name FROM courses

you need to modify it to join to the grade table:

SELECT c.Name
FROM Grade g
LEFT JOIN Courses c ON c.CourseID=g.CourseID
WHERE g.StudentID={$studentID}

you can remove the line breaks -- that just made it easier to read. $studentID is a variable that you should create from $_GET['student'] (with mysql_real_escape_string(), because we're also sending raw user input to the database otherwise):

$studentID = mysql_real_escape_string($_GET['student']);

you may notice, however, that if you view your subjects.php script without a query string set, that you could get a warning/notice that $_GET['student'] doesn't exist. we can do simple validation when defining this variable then:

$studentID = isset($_GET['student']) ? $_GET['student'] : 0;

this is essentially the shorthand equivalent of the following:

if(isset($_GET['student'])){
  $studentID = $_GET['student'];
}else{
  $studentID = 0;
}

whichever you use doesn't matter. then, your query will run with a studentID of 0 (which will most likely never exist), and just won't return any results. you could also display some sort of error message.

if(!$studentID){
  echo "You didn't pick a student.";
}else{
  // the rest of your script would basically go here
}

because 0 evaluates to false in PHP, we don't need to explicitly check if $studentID is equal to zero ($studentID == 0), and instead we can just check if $studentID evaluates to false (!$studentID).

hope that made some sense.