Como faço para exibir o tempo de execução de uma consulta MySQL em PHP?

    $db->query('set profiling=1'); //optional if profiling is already enabled
    $db->query($_POST['query']);
    $stmt = $db->query('show profiles');
    $db->query('set profiling=0'); //optional as well

    $records = $stmt->fetchAll(PDO::FETCH_ASSOC);

    $errmsg = $stmt->errorInfo()[2]; //Output the error message 

$db->query('set profiling=1'); //optional if profiling is already enabled
$db->query($_POST['query']);
$res = $db->query('show profiles');
$records = $res->fetchAll(PDO::FETCH_ASSOC);
$duration = $records[0]['Duration'];  // get the first record [0] and the Duration column ['Duration'] from the first record

Query_ID    Duration    Query   
1           0.00010575  SELECT DATABASE()