php - Select multiple not working -

i have select dropdown in html won't select multiple values. here code have this:

<div class="col-sm-10">               <select multiple id="cmbservice" name="cmbservice" class="form-control" >         <option value="0">- select 1 -</option>             <?php                                                        try{                     $dbhost = "localhost";                     $dbuser = "mdchadmin";                     $dbpass = "123456";                     $dbname = "mdch_new";                      $conn = new mysqli($dbhost, $dbuser, $dbpass, $dbname);                     if ($conn->connect_error) {                         die("connection failed: " . $conn->connect_error);                     }                      $sql = "select promo_number, promo_name promos status=1";                     $result = $conn->query($sql);                     if ($result->num_rows > 0) {                         while($row = $result->fetch_assoc()) {                             echo "<option value=\"{$row['promo_number']}\">{$row['promo_name']}</option>";                         }                     }                                                            $conn->close();                  }catch (exception $e) {                     echo 'error: ' . $e->getmessage();                 }                                                        ?>     </select> </div> 

edit: works answer. have new problem(kinda) , i'm going thru this

so did u suggested, , im getting $customer array in other php file results to:

te,gian marco.'_'.1235 g,g.'_'.123  1235 , 123   data on mobile numbers column. problem , when   $mobile=(explode("_",$customers)); doesn't give me when output via:   foreach($mobile $z) { echo $z; echo "<br>";} 

@identity unknown

you need add square bracket in name attribute name="cmbservice[]"

 <select id="cmbservice" name="cmbservice[]" class="form-control multiple " >