so I recently switched to use pdo instead of mysqli. now I have a question about binding key values with mysqli. I looped through it escaped the key's and values and used them in my queries now I want to do the same thing in pdo but this isn't working and I don't know why this is my code: 

```
foreach($userdata as $key => $value){
    $sql = $this->db->prepare("UPDATE `users` SET :key = :value WHERE `id` = :userid");
    $sql->execute(
        array(
            'key' => $key,
            'value' => $value,
            'userid' => $userid
        )
    );
}

```

ofcourse there's more code to see if it needs update and other type of inputs that need more validation but this is the main query i used but without binding. is this possible with pdo and binding parameter's and values? 
this is the error i'm getting: 

```
SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'username' = 'sjerdus' WHERE `id` = '2'' 

```