没有结果使用预处理语句

Question

当我想创建一个简单的选择和预处理语句但结果我只是得到NULL :(当我做没有准备的语句一切工作正常。

<?php 
    class DbHandler{ 
    public function select($columns, $table_name, $alias, $where, $order){ 
     //echo(phpinfo()); 

     $db = new mysqli("localhost", "root", "", "superhelden"); 
     if(!$db){ 
     exit("Verbindungsfehler: ".mysqli_connect_error()); 
     } 

     if(empty($columns)){ 
     $columns = "*"; 
     trigger_error("No columns chosen. Value set to *.", E_USER_WARNING); 
     } else{ 
     $prepColumns = $columns; 
     } 

     if(empty($table_name)){ 
     trigger_error("Tablename must not be empty.", E_USER_ERROR); 
     } 

     if(empty($where)){ 
     trigger_error("WHERE is empty so no conditions are set. All entries will be selected.", E_USER_WARNING); 
     } 

     //I don't know why but I can't use a param for the tablename 
     $query = "SELECT ? FROM $table_name"; 

     if(!empty($alias)){ 
     $query .= " AS ?"; 
     } 

     if(!empty($where)){ 
     $query .= " WHERE ?"; 
     } 

     //This is working.. 
     $query1 = "SELECT name FROM karten WHERE name='Fausthieb'"; 
     $res = $db->query($query1); 
     while($row = $res->fetch_assoc()){ 
     echo($row["name"] . "<br>"); 
     } 
     //.... :(

     if(empty($order)){ 
     //Show created query 
     echo("$query || "); 
     if($prep = $db->prepare($query)){ 
      if(!empty($alias)){ 
      if(!empty($where)){ 
       $prep->bind_param("sss", $prepColumns, $alias, $where); 
      } else{ 
       $prep->bind_param("ss", $prepColumns, $alias); 
      } 
      } else if(!empty($where)){ 
      //Show params of function 
      echo("columns: $prepColumns || "); 
      echo("Where: $where || "); 
      $prep->bind_param("ss", $prepColumns, $where); 
      } else { 
      $prep->bind_param("s", $prepColumns); 
      } 
//   print_r($prep->result_metadata()); 
//   echo(var_dump($prep)); 
      $prep->execute(); 
      var_dump($prep->error); 
      echo(" || "); 
      $prep->bind_result($result); 
      $prep->fetch(); 
      echo(gettype($result)); 
      $prep->close(); 
     }else{ 
      var_dump($db->error); 
     } 
     } else { 
     $query .= " ORDER BY ?"; 
     if($prep = $db->prepare($query)){ 
      if(!empty($alias)){ 
      if(!empty($where)){ 
       $prep->bind_param("ssss", $prepColumns, $alias, $where, $order); 
      } else{ 
       $prep->bind_param("sss", $prepColumns, $alias, $order); 
      } 
      } else if(!empty($where)){ 
       $prep->bind_param("sss", $prepColumns, $where, $order); 
      } else { 
       $prep->bind_param("ss", $prepColumns, $order); 
      } 

      $prep->execute(); 
      $prep->bind_result($result); 
      $prep->fetch(); 
      echo($result); 
      $prep->close(); 
     }else{ 
      var_dump($db->error); 
     } 
     } 
    } 
    } 
?> 

此代码是打电话给我的选择功能：

include("DbHandler_dominic.php"); 

$test = new DbHandler(); 

$test->select("name", "karten", "", "name='Fausthieb'", ""); 

?> 

然后，我就这一个其中工程就好

<?php 
    include("dbconnect.php"); 
    $pepper = "KratzigeStirn?!"; 

    $username = $_POST["username"]; 
    $prep = $db->prepare("SELECT name FROM spieler WHERE name=?"); 
    $prep->bind_param("s", $username); 
    $prep->execute(); 
    $prep->bind_result($user); 
    $prep->fetch(); 
    $prep->close(); 

    $email = $_POST["email"]; 

    $prep = $db->prepare("SELECT email FROM spieler WHERE email=?"); 
    $prep->bind_param("s", $email); 
    $prep->execute(); 
    $prep->bind_result($mail); 
    $prep->fetch(); 
    $prep->close(); 

    if($user == "" && $mail == ""){ 
    $password = password_hash($_POST["password"].$pepper, PASSWORD_BCRYPT); 

    $prep = $db->prepare("INSERT INTO spieler(name, passwort, email) VALUES(?, ?, ?)"); 
    $prep->bind_param("sss", $username, $password, $email); 

    $prep->execute(); 

    $prep->close(); 
    } else if($user == $username){ 
    echo "Benutzer existiert schon.."; 
    } else if($mail == $email){ 
    echo "E-Mail bereits vergeben.."; 
    } 

    $db->close(); 
?> 

。有什么区别？而且我能为了使SELECT做的工作：/

我的DB图和表格属性：

如果我忘了任何需要的信息只是告诉我，我如果可能，请添加:)

Answer 1

这是我使用的PHP类RTmysqli和示例php代码HERE

用法：

$RTmysqli= new RTlib\RTphp\RTmysqli(); 
$RTmysqli->config(DB_HOST, DB_UNAME, DB_PWORD, DB_NAME); 

$result = $RTmysqli->query("SELECT * FROM slider ORDER BY id"); 

if (!empty($result)) { 
    foreach($result as $row) { 
     print "<br>" . $row["id"] . "(" . $row["title"] . ")\n"; 
    } 
} 

希望它能帮助。 :)