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POUsing AJAX to return query results based on drop down box
 

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    <p>I know that this is a popular question and I have looked at many examples trying to get my head around <code>AJAX</code> and <code>jQuery</code>.</p> <p>I have a simple situation with one drop down box when changed sends an <code>AJAX</code> request for the results of an <code>SQL</code> query based on the drop down box selection. </p> <p>The page loads correctly and the function is being called when a department is being chosen from the drop down box (the alert tells me that) but I am not getting any return data. In trying to identify the problem how can I tell whether the getTeachers.php file is actually running?</p> <p><strong>Web page</strong> Script for calling getTeacher.php on the server</p> <pre><code>&lt;script src="http://localhost/jquery/jquery.min.js"&gt; &lt;/script&gt; &lt;script&gt; function checkTeacherList(str) { var xmlhttp; if (str=="") { document.getElementById("txtTeacher").innerHTML=""; return; } if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp=new XMLHttpRequest(); } else {// code for IE6, IE5 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState==4 &amp;&amp; xmlhttp.status==200) { document.getElementById("txtTeacher").innerHTML=xmlhttp.responseText; } } xmlhttp.open("GET","getTeachers.php?q="+str,true); xmlhttp.send(); alert(str); //To test it is getting this far, which it does } &lt;/script&gt; </code></pre> <p>Drop down box and txtTeacher ID for return data from server</p> <pre><code>&lt;select name="department_list" id="department_list" onchange="checkTeacherList(this.value);" &gt; &lt;?php $options[0] = 'All'; $intloop = 1; while($row = mysql_fetch_array($department_result)) { $options[$intloop] = $row['departmentName']; $intloop = $intloop + 1; } foreach($options as $value =&gt; $caption) { echo "&lt;option value=\"$caption\"&gt;$caption&lt;/option&gt;"; } ?&gt; &lt;/select&gt; &lt;div id="txtTeachers"&gt;Teacher names&lt;/div&gt; </code></pre> <p><strong>Server side PHP - getTeachers.php</strong></p> <pre><code>&lt;?php $q=$_GET["q"]; $con = mysql_connect('localhost', 'root', ''); if (!$con) { die('Could not connect: ' . mysql_error($con)); } $db_selected = mysql_select_db("iobserve"); $sql="SELECT * FROM departments WHERE departmentName = '".$q."';"; $result = mysql_query($sql); while($row = mysql_fetch_array($result)) { echo $row['teacherName']; } mysql_close($con); ?&gt; </code></pre>
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    1. COTo test if the file is run at all you can respond with some hard coded dummy-data, instead of running code that might fail.
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      1. USMarcus
    2. COThanks - it turned out that I needed to put the full path in to the php file. I was running it from WordPress and it must have been struggling to locate it.
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    3. COplease add mysql_real_escape_string to your select query if you don't want that everybody can drop you database.
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