Pokus.PHP

<?php
$server = "localhost";
$user = "uzivatel";
$pass = "heslo";
$db = "jmeno_databaze";
$mysqli = mysqli_connect($server, $user, $pass, $db); //připojení k MySQL
$sql = 'SELECT * FROM arduino_ovladani WHERE modul="led"';
$doSql = $mysqli->query($sql);
if($doSql->num_rows == 0){
$sql = 'INSERT INTO arduino_ovladani (modul, hodnota) VALUES ("led", 0)';
$doSql = $mysqli->query($sql);
}
if(isset($_POST['odeslano'])){ //pokud byl formulář odeslán
$hodnota = sanitize($_POST['stav']);
$sql = 'UPDATE arduino_ovladani SET hodnota="'.$hodnota.'" WHERE modul="led"';
$doSql = $mysqli->query($sql);
if($hodnota == 1){
echo 'Zapnuto';
}
else{
echo 'Vypnuto';
}
echo '<br /><br />';
}
$sql = 'SELECT * FROM arduino_ovladani WHERE modul="led"';
$doSql = $mysqli->query($sql);
$hodnota = $doSql->fetch_assoc()['hodnota']; //načte hodnotu led z DB
$zapnutoChecked = $hodnota == 1 ? 'checked' : ''; //nastaví výchozí hodnotu radio buttonu
$vypnutoChecked = $hodnota == 0 ? 'checked' : '';
echo '<form action="" method="POST" >';
echo '<input type="hidden" value="1" name="odeslano" />';
echo '<input type="radio" name="stav" value="1" '.$zapnutoChecked.' /> Zapnout<br>';
echo '<input type="radio" name="stav" value="0" '.$vypnutoChecked.' /> Vypnout<br><br>';
echo '<input type="submit" value="Odeslat">';
echo '</form>';
function sanitize($input){
$input = htmlspecialchars($input);
$input = htmlentities($input);
$input = strip_tags($input);
$input = trim($input);
return $input;
}
?>

Note: When a user clicks on a radio-button, it becomes checked, and all other radio-buttons with equal name become unchecked.