$fmcourse = $_POST['fm_courses'];
    $student_id = $_POST["id"];
    $batch_id = $_POST["name"];
    delete_enrollments( $student_id, $batch_id );

    foreach($fmcourse as $fmc) {
        $course_id = $fmc;

        if( record_exists( $student_id, $course_id, $batch_id ) == FALSE ) {
            $stmt = mysqli_prepare($conn, "INSERT INTO enrollments (enrollment_id, student_id, course_id, batch_id, is_deleted, joining_date) VALUES( NULL, ?, ?, ?, 0, NOW() );");
            $is_binded = mysqli_stmt_bind_param($stmt, "iii", $student_id, $course_id, $batch_id);
            $is_exec = mysqli_stmt_execute($stmt);
            mysqli_stmt_close($stmt);
        }
        else {
            undelete_enrollment($student_id,  $course_id, $batch_id);
        }
    }

    function undelete_enrollment($student_id,  $course_id, $batch_id) {
        global $conn;
        $stmt = mysqli_prepare($conn, "UPDATE enrollments SET is_deleted = 0, joining_date = NOW() WHERE student_id= ? AND course_id = ? AND batch_id = ?");
        $is_binded = mysqli_stmt_bind_param($stmt, "iii", $student_id, $course_id,$batch_id);
        $is_exec = mysqli_stmt_execute($stmt);
        mysqli_stmt_close($stmt);
        return $is_exec;
    }

    function record_exists( $student_id,  $course_id, $batch_id ) {
        global $conn;

        $stmt = mysqli_prepare($conn, "SELECT COUNT(enrollment_id) as total FROM enrollments WHERE student_id= ? AND course_id = ? AND batch_id = ?");
        $is_binded = mysqli_stmt_bind_param($stmt, "iii", $student_id, $course_id, $batch_id);
        $is_exec = mysqli_stmt_execute($stmt);
        $result = mysqli_stmt_get_result($stmt);
        $record = mysqli_fetch_assoc($result);
        mysqli_stmt_close($stmt);
        return ( isset( $record['total'] ) AND $record['total'] > 0 );
    }

    function delete_enrollments( $student_id, $batch_id ) {
        global $conn;
        $stmt = mysqli_prepare($conn, "UPDATE enrollments SET is_deleted = 1 WHERE student_id = ? AND batch_id =?;");
        $is_binded = mysqli_stmt_bind_param($stmt, "ii", $student_id, $batch_id);
        $is_exec = mysqli_stmt_execute($stmt);
        mysqli_stmt_close($stmt);
        return $is_exec;
    }