php - Ajax fetches data from database only once -

i working in wordpress , have drop down box , search button. , have used ajax fetch data after selecting choice drop down box. problem search button fetches data once , second time if select drop down other value , press search refreshed data not pasted.

html

[showmyimage] <form id="mydispimage" action="" method="post"> <select name="category" id="category" style="width:250px; background-color:lightgrey;">'; <option value="" disabled="disabled" selected="selected" ">select category</option>'; <option value="cutie pie">cutie pie</option>'; <option value="chubby">chubby</option>'; <option value="dimples">dimples</option>'; </select>;  <input type="submit" id="displayimage" name="displayimage" value="search"  style="margin-left:15px; margin-bottom:15px;"> </form> <div id="myresult"></div> 

ajax code

jquery(function ($) {     $("#mydispimage").submit(function (e) { //form intercepted         e.preventdefault(); //$("#displayimage").change(function (){  alert("hello");         //serialize form contains secretcode         var sentdata = $(this).serializearray();          //add additional param data                 sentdata.push({             name: 'action',             value: 'display'         })          //set sentdata data sent         $.post(yes.ajaxurl, sentdata, function (res) { //start of funciton             //$("#myresult").append(res.l);             $("#myresult").append(res.form);  //$.parsejson(data);             return false;         } //end of function         ,         'json'); //set datatype json, parsed data in callback     });  // submit end here      }); // change function }); 

php code

    add_action( 'wp_ajax_display', 'display' );     add_action( 'wp_ajax_nopriv_display', 'display');      add_shortcode('showmyimage','showimage');      function showimage(){       // register & enqueue javascript file called globals.js     wp_register_script( 'displayimg', get_stylesheet_directory_uri() . "/js/ajaxinsert.js", array( 'jquery' ) );      wp_enqueue_script( 'displayimg' );      // use wp_localize_script pass php variables javascript     wp_localize_script( 'displayimg', 'yes', array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) ) ); } function display() {     $response = array();      if(isset($_post['category'])) {          $category = $_post['category'];         $response['l'] = '<a href="" style="margin-top:30px !important; position:absolute; z-index:50; font-size:20px;"> participate </a>';          $response['ujicountdown'] = do_shortcode('[ujicountdown id="photos contest" expire="2015/04/30 00:00" hide="true" url="" subscr="sdf" recurring="" rectype="second" repeats=""]');          global $wpdb;         $votes = 1;          $response["category"] = $category;          //get current competition value         $comp = $wpdb->get_var("select competition competition order cid desc limit 1");          $sql = "select 1user.uid, 1user.username, 1user.competition, 1user.path, 1user.category, sum(votes.votes) votessum 1user left join votes on 1user.uid=votes.uid group 1user.uid, 1user.username, 1user.competition, 1user.path, 1user.category having 1user.category = '$category' && 1user.competition = '$comp' order votessum";          $results = $wpdb->get_results($wpdb->prepare($sql)) or die(mysql_error());          if( is_array($results) && count($results) > 0  ) {              $form = "";             foreach( $results $result ) {                  $form .= '<form action="" method="post">';                 $form .= "<input name='category' type='hidden' value='$result->category'>";                  $form .= "<img src='$result->path' width='150' height='150' >" . '<br><br>';                 $form .= "<input name='id' type='hidden' value='$result->uid'>";                 $form .= "<input name='comp' type='hidden' value='$result->competition'>";                 $form .= $result->username.'<br>';                  $form .= $result->votessum.'<br>';                 $form .= "<input style='margin-bottom:30px;' value='vote' name='submit' type='submit'/></form>";                 }//end of foreach              $response['form'] = $form;         }      echo json_encode($response);     die();      }//end of isset     else {         $respons["status"] = false;         $response["message"] = "<h1 style='font-family:satisfy,cursive; font-size:normal;background-color:pink;'>"."please select category"." </h1>";          echo json_encode($response);         die();     }   }