使用SELECT函数时，mysql不会全部选择

My code looks like this:

我的代码看起来像这样:

$sql = "SELECT `sw1`, `sw2`, `sw3`, `sw4`, `fb1`, `fb2`, `fb3`, `fb4`, `bew1`, `bew2`, `bew3`, `bew4` FROM `reg` WHERE `id` = ".$id." ORDER BY `id` ASC LIMIT 0, 30 ";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        foreach($row as $x => $x_value) {
             echo "Key=" . $x . ", Value=" . $x_value;
             echo "<br>";
        }
    }
}
$sql =