How to set automatically id base on date - php

Question

I'm a newbie in PHP. I hope someone can help me. before that sorry my english's bad.
I want set kd_transaksi base on date and id from another table. when people booking, system automatically set kd_transaksi.
$tgl_pesan = date("Ymd");
$cek = mysqli_query($conn, "SELECT max(kd_booking) AS kode FROM booking WHERE kd_booking LIKE '$tgl_pesan%'");
$row = mysqli_fetch_array($cek);
$kdMax = $row['kode'];
$nourut = substr($kdMax, 8, 4);
$nourut++;
$char = "BO";
$kd_transaksi = $char.$tgl_pesan.printf('%04s', $nourut);
$kd_booking = mysqli_insert_id($conn);
$book = "INSERT INTO detail_booking (kd_booking,kd_transaksi,total_bayar) VALUES ('".$kd_booking."','$kd_transaksi',$total_bayar')";
$ok = mysqli_query($conn,$book);
if ($ok) {
header('location:../mybooking.php');
} else{
mysqli_close($conn);
}
but result in query $cek is NULL.
$cek = mysqli_query($conn, "SELECT max(kd_booking) AS kode FROM booking WHERE kd_booking LIKE '$tgl_pesan%'");
how do I fix it?
booking table
CREATE TABLE `booking` (
`kd_booking` int(11) NOT NULL,
`id_user` int(11) NOT NULL,
`kd_paket` int(11) NOT NULL,
`jml_org` int(11) NOT NULL,
`tgl_pesan` date NOT NULL,
`tgl_wisata` date NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
What i want is
If someone booking today and get kd_booking 21, then the output would be : BO2018120521.

Answer 1

First of all, you have something wrong with your CREATE TABLE. When you create a table you should have an AUTOINCREMENT primary key, this is your id. So it would be something like this:
CREATE TABLE `booking` ( `id` INT NOT NULL AUTO_INCREMENT , `id_user` INT(11) NOT NULL , `kd_paket` INT(11) NOT NULL , `jml_org` INT(11) NOT NULL , `tgl_wisata` DATE NOT NULL , `tgl_pesan` DATE NOT NULL , PRIMARY KEY (`id`)) ENGINE = InnoDB;
As i can se you have two errors:
Date should be like date('Y-m-d') http://php.net/manual/en/function.date.php
You're trying to insert an int value like '".$kd_booking."' when that just works for strings.
Hope it helped.