Deleting and redirecting to the same page

Question

Hello I have this delete function and I don't have any function set on it yet because I want to delete the data and redirect in the same page but I don't know how I tried researching but it doesn't work. In this page all of the information shown was sent from a page to this page in order for the user to view the schedule then have the option of deleting it but I don't know how to delete data and redirect into the same page without messing up the other data being shown..I tried using the header(location:) function but the moment I redirect the data that is shown there is not being shown because I did not pass any value while redirecting need help here, this is my code

if ($teacher<>""){
    $query1 = mysqli_query($conn," SELECT *  from schedule natural join instructor where day ='t' and schedule.instructorID ='$teacher' and timeID ='$id' and grade = '$grade' and semester = '$semester'");
}
elseif ($room<>""){
    $query1 = mysqli_query($conn,"SELECT * from schedule  natural join instructor where day = 't' and  schedule.room = '$room' and timeID ='$id' and grade = '$grade' and semester = '$semester'");
}
elseif ($strand<>""){
    $query1 = mysqli_query($conn,"SELECT * from schedule  natural join instructor where day = 't' and  schedule.strand= '$strand' and timeID ='$id' and grade = '$grade' and semester = '$semester'");
}
$row1 = mysqli_fetch_array($query1);
$id1 = $row['scheduleID'];
$count=mysqli_num_rows($query1);
if ($count==0)//checking
{
    //echo "<td></td>";

}
else
{
    //print 
    echo "<li class='showme'>"; 
    echo "<a href='#' id='$id1' class='delete' title='Delete'>Remove</a>";
    echo $row1['subject'];
    echo "</li>";
    echo "<li class='$displayc'>$row1[strand]</li>";
    echo "<li class='$displaym'>$row1[fname], $row1[lname]</li>";                                           
    echo "<li class='$displayr'>Room $row1[room]</li>";

    echo "</ul>";
    echo "</div>";
}   
?>
</td>

then I have the delete.php but I don't have any set function in there yet since it I only know how to delete using the form but the redirecting is the problem when you delete because of the reason stated above

Answer 1

Big security flaw: SQL Injection Use prepared statements for your queries

In your header location, just append a query string .

The query string can be retrieved with :

$grade = int($_GET['grade']);
$semester = int($_GET['semester']);

Where grade and semester are the parameter name. Note that the $_GET[...] thingy has been wrapped with int(...) for sanitation purposes. This ensure that $grade and semester will be ´int` (numbers).

Your location header should look like: LOCATION: http://yoursite/diplay-page.php?grade=7&semester=8

Also, when displaying, escape your data! Right now, you are vulnerable to XSS injections .

If you do not know how, start with OWASP advices : https://www.owasp.org/index.php/PHP_Top_5