delete.php

<?php

include 'connection.php';

if (is_array($_POST['username'])){

    // print_r($_POST);

    $username_0 = join(',', $_POST['username']);
    
    $username = "'". str_replace(",","','",$username_0 ) . "'";

    $sql = "delete from user where username in($username)";

    $result = mysqli_query($conn, $sql);

    if ($result) {

    echo 'delete successfully!';

    header("refresh:2; url= List.php");    
    exit;
    } else {

    echo 'delete unsuccessfully!';

    header("refresh:2; url= List.php");   
    exit;
    }

}elseif (is_string($_GET['username'])) {

    $username ="'" . $_GET['username'] . "'";

    $sql = "delete from user where username in($username)";

    $result = mysqli_query($conn, $sql);

    if ($result) {

    echo 'delete successfully!';

    header("refresh:3; url= List.php");    
    exit;
    } else {

    echo 'delete unsuccessfully!';

    header("refresh:2; url= List.php");   
    exit;
    }


}else{
 echo 'Illegal data!';
 exit;
}

?>