creating student id

<?php

$year = date('y');

$study_year = $year . ($year + 1);

$dept_code = 123;

$year_code = $study_year . $dept_code;

$student_roll = 1;

$student_roll_full_digit = str_pad($student_roll, 3, "0", STR_PAD_LEFT);

$student_id = $year_code . $student_roll_full_digit;

echo $student_id;

/**
 * Mysql code
 */
$year = $_POST['year'];
$dept_code = $_POST['dept_code'];

$query = "SELECT * FROM students WHERE year='' AND dept_code='' ORDER BY id DESC LIMIT 1";

$result = mysqli_query($connection, $query);

$result_exists = mysqli_num_rows($result);

if($result_exists > 0) {
	$row = mysqli_fetch_assoc($result) {
		$student_id = intval($row['student_id']) + 1;
	}
} else {
	$student_id = $year . $dept_code . '001';
}