Error: number of bound variables does not match number of tokens

I want to make an insert only if there's no correspondence in the db (mySQL) but he makes me not the statement. Here's the snippet

    if ($sql->rowCount() > 0) {
        echo 'Non inserisci';
    } else {
        echo 'Inserisci';
        $db->beginTransaction();
        echo 'Ciao3';
        $sql = $db->prepare("INSERT INTO contatti (nome,cognome) VALUES (?,?)") or die('Ciao2');
        echo 'Ciao4';
        $sql->execute(array($_POST['nome'],$_POST['cognome']));
        echo 'Ciao5';
        $db->rollBack();
    }

Where The SELECT is

    $db->beginTransaction();
    $sql = $db->prepare("SELECT * FROM contatti WHERE nome = ? AND cognome = ? WHERE nome = ? AND cognome = ?") or die ('Ciao1');
    $sql->execute(array($_POST['nome'],$_POST['cognome']));
    $db->rollBack();

Can you explain me where's the fault?

The fault is in arithmetics

Let's count tokens:

 SELECT * FROM contatti WHERE nome = ? // one
                       AND cognome = ? // two
                        WHERE nome = ? // three
                       AND cognome = ? // four

now let's count number of bound variables:

array($_POST['nome'], // one
      $_POST['cognome']) // two

4 is apparently not equal to two. that's the problem