title: retrieve data from database mysql not working
body: <p>Hi i am using the html dropdown's onchange event using ajax</p>
  
  <p>In the code i am using, should get the address column value when i change the 
  drop down.</p>
  
  <p>but it is not working.What may have gone wrong?</p>
  
  <p>here is the code </p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
    &lt;script&gt;
       function showUser( str ) {
          if ( str == "" ) {
             document.getElementById("txtHint").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("txtHint").innerHTML=xmlhttp.responseText;
             }
          }
          xmlhttp.open("GET", "getuser.php?q=" + str, true);
          xmlhttp.send();
       }
     &lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  
  &lt;form&gt;    
    &lt;?php
       mysql_connect('localhost', 'tiger', 'tiger');
       mysql_select_db('theaterdb');
       $sql = "select theater_name from theater;";
       $result = mysql_query($sql);
       echo "&lt;select name='theater_name' id='course' onchange='showUser(this.value);'&gt;";
       while ( $row = mysql_fetch_array( $result ) ) {
          echo "&lt;option value='" . $row['theater_name'] ."'&gt;" . $row['theater_name']. "&lt;/option&gt;";
       }
       echo "&lt;/select&gt;";
  ?&gt;
  
  &lt;/form&gt;
  
  &lt;br&gt;
  &lt;div id="txtHint"&gt;&lt;b&gt;Info&lt;/b&gt;&lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt; 
  </code></pre>
  
  <p>Code for getuser.php</p>
  
  <pre><code>&lt;?php
     $q = $_GET["q"];
     $con = mysqli_connect("localhost", "tiger", "tiger", "theaterdb");
     if ( !$con ) {
        die('Could not connect: ' . mysqli_error( $con ) );
     }
  
     mysqli_select_db( $con );
     $sql = "SELECT address FROM theater WHERE theater_name = '".$q."'";
  
     $result = mysqli_query( $con, $sql );
  
     echo "&lt;table border='1'&gt;
       &lt;tr&gt;
          &lt;th&gt;Firstname&lt;/th&gt;
       &lt;/tr&gt;";
  
       while( $row = mysqli_fetch_array( $result ) ) {
         echo "&lt;tr&gt;";
            echo "&lt;td&gt;" . $row['address'] . "&lt;/td&gt;";
         echo "&lt;/tr&gt;";
      }
    echo "&lt;/table&gt;";
    mysqli_close($con);
  ?&gt; 
  </code></pre>