Working Example Of A 3 Login Limit For A Website

login limit

if (isset($_POST['submit']))
{
	$datetime = date('Y-m-d H:i:s');
	$username = htmlentities(trim(mysqli_real_escape_string($dbc,$_POST['username'])));
	$check_user = mysqli_query($dbc,"SELECT * FROM attempts WHERE user='$username'");
	$ip = $_SERVER['REMOTE_ADDR'];
	if (mysqli_num_rows($check_user) > 0)
	{
		$date_check = mysqli_query($dbc,"SELECT * FROM attempts WHERE user='$username' AND datetime > (NOW() - INTERVAL 30 MINUTE)");
		$date = mysqli_fetch_assoc($date_check);
		if ($_POST['username'] == $date['user'] && $date['attempt'] == 0)
		{
			mysqli_query($dbc,"UPDATE attempts SET attempt=1 WHERE datetime > (NOW() - INTERVAL 30 MINUTE)");
		}
		else if ($_POST['username'] == $date['user'] && $date['attempt'] == 1)
		{
			mysqli_query($dbc,"UPDATE attempts SET attempt=2 WHERE datetime > (NOW() - INTERVAL 30 MINUTE)");
		}
		else if ($_POST['username'] == $date['user'] && $date['attempt'] == 2)
		{
			mysqli_query($dbc,"UPDATE attempts SET attempt=3 WHERE datetime > (NOW() - INTERVAL 30 MINUTE)");
		}
		else if ($_POST['username'] == $date['user'] && $date['attempt'] == 3)
		{
			echo 'To many attempts';
		}
	}
	else
	{
		mysqli_query($dbc,"INSERT INTO `attempts` (`user`,`ip`,`attempt`,`datetime`) VALUES ('$username','$ip',0,'$datetime')");
		echo 'Field Added';
	}	
}
?>
<form method="post">
	Username: <input type="text" name="username" placeholder="username" />
	<input type="submit" name="submit" value="Submit" />
</form>