validation to check database
$("#registerForm").validate({

            rules: {

                BCNumber : { required: true, minlength: 5, maxlength: 10 },
                Username : { required: true, minlength: 5, maxlength: 10 },
                Password : { required: true, minlength: 5, maxlength: 10 },
                SecurityQuestion : { required: true, minlength: 5, maxlength: 10 },
                SecurityAnswer : { required: true, minlength: 5, maxlength: 10 },

            }

$("#registerForm").submit(function(){
 var  id=//find the value to be checked
   $.get("url?id="+id,function(data){
       if(data=="valid"){
          //submit the form
          }else
             {
            return false;
             }
      })
})

$("#registerForm").validate({
        rules: {
            Username : {
              required: true,
              minlength: 5,
              maxlength: 10,
              remote: 'check_username.php'
            }
        }
});