Generating admission number using id in MYSQL. I want code from CodeIgniter - codeigniter

Question

In my project, I have a student id no. It should auto increment. I want to auto-generate an admission number. How do I do it?
This is my controller
$insert_id = $this->student_model->add($data);
$data_new = array(
'student_id' => $insert_id,
'class_id' => $class_id,
'section_id' => $section_id,
This is my model
public function add($data) {
if (isset($data['id'])) {
$this->db->where('id', $data['id']);
$this->db->update('students', $data);
} else {
$this->db->insert('students', $data);
return $this->db->insert_id();
}
}
Here is my view
<form id="form1" action="<?php echo site_url('student/create') ?>" id="employeeform" name="employeeform" method="post" accept-charset="utf-8" enctype="multipart/form-data">
<div class="box-body">
<div class="tshadow mb25 bozero">
<h4 class="pagetitleh2"><?php echo $this->lang->line('student'); ?> <?php echo $this->lang->line('admission'); ?> </h4>
<div class="around10">
<?php if ($this->session->flashdata('msg')) { ?>
<?php echo $this->session->flashdata('msg') ?>
<?php } ?>
<?php echo $this->customlib->getCSRF(); ?>
<input type="hidden" name="sibling_name" value="<?php echo set_value('sibling_name'); ?>" id="sibling_name_next">
<input type="hidden" name="sibling_id" value="<?php echo set_value('sibling_id',0); ?>" id="sibling_id">
<div class="row">
<div class="col-md-3">
<div class="form-group">
<label for="exampleInputEmail1"><?php echo $this->lang->line('admission_no'); ?></label> <small class="req"> *</small>
<input autofocus="" id="admission_no" name="admission_no" placeholder="" type="text" class="form-control" value="<?php echo set_value('admission_no', date($this->customlib->getSchoolDateFormat())); ?>" name="admission_no" class="form-control">
<span class="text-danger"><?php echo form_error('admission_no'); ?></span>
</div>
Here admission number put manually, but I want it auto-created. I don't know how to do. I'm new with CodeIgniter.
My database
My form view

Answer 1

if you want to add unique admission you must chick the admission or use this query
$this->db->order_by('admission_no','DESC');
$this->db->get('students',1)->row()->admission_no + 1;
Put the bellow code in your view in your admission input which id of it is id="admission_no" romove the input and copy paste the code. this get the lastest admission no and then add 1 to the admission no also you can remove this value and add manually another value. that must be unique
<?php
$this->db->order_by('admission_no','DESC');
$auto-add = $this->db->get('students',1)->row()->admission_no + 1;
?>
<input autofocus="" id="admission_no" name="admission_no" placeholder="" type="text" class="form-control" value="<?php echo $auto-add; ?>" class="form-control">