数据库设计随意设计吧 反正就是用户可以存入就可以了！

正文tp后台方法简化：

 //用户验证   function checknm($name){       $info = D('user')->where("user_name ='$name'")->find();       //dump($info);die;       $flag = '';       if($info){          echo 1;                }else{          echo 2;               }   }

后台返回1和2

前端ajax部分 用data接收1和2的状态

当然data的接收 主要看你后台传的是什么格式的数据类型了！这个大家可以百度ajax了！

     
                          
      
                               
       
                                
        
                                 
                                  
         
                                                                          
          
                                            
           
                                                                           function checkname(){                                        var name = document.getElementById('User_username').value;                                                                            $.get('/tpTest/index.php/User/checknm',{name:name},function(data){                                            //alert(name);                                         if(data == 1){                                           var nm = document.getElementById('span1');                                           nm.innerHTML='用户名存在';                                           nm.className ="msg2";                                         }                                         if(data == 2){                                         var nm = document.getElementById('span1');                                           nm.innerHTML='用户可以使用';                                           nm.className ="msg";                                                                                  }                                        })                                                               }                                                                                                                                                    
            
                                                     
             
              用户名