I trying to update my db using a PDO statement, I have had no real problems until I try to update it using variables as the name and field . 

```
    $real_function = 'top' ;
    $value = 99 ;
    $tableName = "twitter_control" ;

    $stmt = $pdo->prepare("UPDATE ? SET ?=? WHERE id='control' ");
    $stmt->execute(array( $tableName, $real_function, $value ));

```

If I use this code all works as expected 

```
  $stmt = $pdo->prepare("UPDATE twitter_control SET top=? WHERE id='control' ");
  $stmt->execute(array( $value ));

```

How can I make this work ? , any suggestions please ?