MYSQL PDO COUNT(*)

$count = $db->query("SELECT COUNT(*) FROM users")->fetchColumn();

OR

$stmt = $db->prepare("SELECT COUNT(*) FROM users WHERE uid=:uid");
$result = $stmt->execute(array(':uid' => $uid)); 
$count = $stmt->fetchColumn();

OR

$stmt = $db->prepare("SELECT COUNT(*) FROM friends WHERE uid=:uid OR fid=:uid");
$stmt->bindValue(':uid', $uid, PDO::PARAM_INT);
$stmt->execute();
$count = $stmt->fetchColumn();