Undefined indexes and possible missing retrieval php

Question

I've gotten into a bigger problem now. Whenever I want to select for intake and subjects, it will show undefined index: intake and Undefined index: programme respectively. It also did not display options for subjects when I select other choices for intake even though my database contains data for it. Is my code not able to retrieve it or is it something else?Result Image: Errors Need help thanks

 <?php
    include "..\subjects\connect3.php";
    //echo "Connection successs";

    $query = "SELECT * FROM programmes_list";
    $result = mysqli_query($link, $query);
    ?>

    <form name = "form1" action="" method="post">
    <table>
    <tr>
    <td>Select Pragramme</td>
    <td><select id="programmedd" onChange="change_programme()">
    <option>select</option>
    <?php
    while($row=mysqli_fetch_array($result)){
        ?>
    <option value="<?php echo $row["ID"]; ?>"><?php echo $row["programme_name"]; ?></option>
    <?php
        }
        ?>
        </select></td>
        </tr>

        <tr>
            <td>Select intake</td>
            <td>
            <div id="intake">
            <select>
            <option>Select</option>
            </select>
            </div>
            </td>
        </tr>

        <tr>
            <td>Select Subjects</td>
            <td>
            <div id="subject">
            <select>
            <option>Select</option>
            </select>
            </div>
            </td>
        </tr>


    </table>
    </form>




    <script type="text/javascript">
    function change_programme()
    {
        var xmlhttp=new XMLHttpRequest();
        xmlhttp.open("GET","ajax.php?programme="+document.getElementById("programmedd").value,false);
        xmlhttp.send(null);

        document.getElementById("intake").innerHTML=xmlhttp.responseText;

    }


        function change_intake()
    {
        var xmlhttp=new XMLHttpRequest();
        xmlhttp.open("GET","ajax.php?intake="+document.getElementById("intakedd").value,false);
        xmlhttp.send(null);

        document.getElementById("subject").innerHTML=xmlhttp.responseText;
    }
    </script>



    //ajax.php
    <?php
        $dbhost = 'localhost' ;
        $username = 'root' ;
        $password = '' ;
        $db = 'programmes' ;

        $link = mysqli_connect("$dbhost", "$username", "$password");

        mysqli_select_db($link, $db);

        $programme=$_GET["programme"];
        $intake=$_GET["intake"];

    if ($programme!="")
    {
        $res=mysqli_query($link, "select * from intakes where intake_no = $programme");
        echo "<select id='intakedd' onChange='change_intake()'>";

        while($value = mysqli_fetch_assoc($res))
        {

        echo "<option value=".$value['ID'].">";
        echo $value["intake_list"];
        echo "</option>";
        }   
        echo "</select>";
    }

    if ($intake!="")
    {
        $res=mysqli_query($link, "select * from subject_list where subject_no = $intake");
        echo "<select>";

        while($value = mysqli_fetch_assoc($res))
        {

        echo "<option value=".$value['ID'].">";
        echo $value["subjects"];
        echo "</option>";
        }   
        echo "</select>";
    }

        ?>

Answer 1

The reason you're getting an undefined index notice is because change_programme() only sends a ?programme= in the call to ajax.php, and change_intake() only sends a ?intake= in the call. However, in ajax.php, you're trying to get both from $_GET.

So, the call made from change_programme() will give you an undefined index notice for $_GET['intake'], because it really isn't supplied in the URL. The call made from change_intake() will give you an undefined index notice for $_GET['programme'], for the same reason.

You can fix this by checking if they're set:

$programme = isset($_GET["programme"]) ? $_GET["programme"] : "";
$intake = isset($_GET["intake"]) ? $_GET["intake"] : "";

This is shorthand for:

if (isset($_GET["programme"])) {
    $programme = $_GET["programme"];
} else {
    $programme = "";
}

if (isset($_GET["intake"])) {
    $intake = $_GET["intake"];
} else {
    $intake = "";
}

As a side note, never trust any input you get from a URL, especially if you're going to use it directly in a query. Please pass the $programme and $intake variables through mysqli_real_escape_string() first Please use a prepared statement with bound parameters instead, to reduce the chance of SQL injection attacks.