Recuperando dados através do mysql usando função e uso na caixa de seleção?

function selectdata(){
   $select="SELECT * FROM table_name";

   $run=mysql_query($select);
   $field_name = '';
   while($fetch=mysql_fetch_array($run)){
       $field_name.="<option value=''>" . $fetch['field_name'] . "</option>";
   }
   return $field_name;
}

<select name="office_name">
<?php echo selectdata(); ?>
</select>