如何修复，发布未插入的值。 mysql列是空的

I have php page that you can type in a number and then click the submit button and it should insert the column in the table. The problem I have is that it isn't inserting the value but just leaving an empty field.

Function 1 post values clean

function post($name)
{
    if (isset($_POST[$name]))
    {

        if (is_array($_POST[$name]))
        {
            return array_map(function($item){      
            return htmlspecialchars(trim($item));
            }, $_POST[$name]);
        }

        return htmlspecialchars(trim($_POST[$name]));
    }
}

Function 02

function post_form(...$except_these)
{
    unset($_POST['submit']);
    $post_form = [];
    $error = false;

    foreach($_POST as $key => $value){

        if ( !in_array($key, $except_these) && !post($key) )
        {
            $error = true;

        } else {

            $post_form[$key] = post($key);
        }

    }


    if ( $error )
    {
        return false;
    }

    return $post_form;
}

post

$_POST['submit'] = 1;
$_POST['user_name'] = 'Arman';
$_POST['user_email'] = 'abc';
$_POST['user_password'] = '1234';

insert

$post_form = post_form('submit');


$query = $db->prepare("INSERT INTO users SET
    user_name = ?,
    user_email = ?,
    user_password = ?
");

$insert = $query->execute($post_form);

no error message but mysql columns is empty.