Question

Basically i have a form where a studentID is inputted, i then want to check id the inputted studentID is in the database, if it is post the form to the next page. If not then display an error on the page where you input studentID

Don’t really know where to start
Cheers

Answer 1

is this what you want?

<form id = "form" action = "./?page=markandfeedback" method = "post"> 

    <br>
    Mark for:
<INPUT id="stud" onkeypress="return isNumberKey(event)" type="text" name="stud"  value="Enter Student Number">
<input type="submit" value = 'Continue'>
<?

$studID = $_POST['stud'];
$module2 = $_SESSION['module'];
$ex = $_POST['exer'];
$studerr = array();

$sql = 'SELECT * FROM `student`, `modules` WHERE `studentID` = '.$studID.' AND `moduleCode` = '.$_SESSION['module'];
$result = mysql_query ($sql);
//    echo $_SESSION['module'];

if ($result == NULL) { // nothing found
echo "the student id you entered is not in the database";
}
else {


$_SESSION['student'] = $studID;

Header("Location: http://www.whereever.com/"); // send the browser where you want
exit();
}
?>

EDIT:
I went over the other answers. I assume you check for mysql injection properly. I recommend implementing AJAX AFTER everything works and is secure. The idea behind my solution was to solve the problem as simple as possible. If you want to make something fancy out of it you could:

• generate the whole form via php and tell the user in the input field, that the id wasn’t found
• tell your Javascript to present the information in some fancy way
• Use AJAX. Everybody loves forms with AJAX.
• You could, as suggested, assume that the user entered a valid id. You would check on the “whereever” page wether the id is actually valid. If it weren’t, you would simply send the user back to the form and tell the php to output an error message (maybe via get). This possibility is not usual, I am not sure if it has any advantages.

the mysql_num_rows hint is nice, too, if you don’t want any data from the user. I thought you wanted to do something with the data because of the SELECT *.