Can not add automatic numbers behind with php - php

Question

I have the code from the database, the data should appear automatically in sequence. the code is composed of text and number like this CO-00001 but when I generate the code it just adds one digit in the back but not add the value of example CO-00001 to CO-000001 how to solve it?
ex :
$id = 0902340
$query = "SELECT substr(code_id,3,5) as cd FROM tb_inv WHERE substr(code_id,3,5) = '".$id."' ORDER BY code_id DESC LIMIT 1";
$get_id = $this->db->query($query);
$show_id = $get_id->num_rows();
$new_code = $get_id->row();
if($show_id > 0){
$new = $new_code->cd + 1;
$fix_code = $new;
}else{
$fix_code = 'CO-00001';
}

Answer 1

you can't do algebra on alphabets, therefore you need to split the alphabets and the numerics like so:
$id = 0902340
$query = "SELECT substr(code_id,3,5) as cd FROM tb_inv WHERE substr(code_id,3,5) = '".$id."' ORDER BY code_id DESC LIMIT 1";
$get_id = $this->db->query($query);
$show_id = $get_id->num_rows();
$new_code = $get_id->row();
if($show_id > 0){
$prefix = substr($new_code->cd, 0, 3); // get the prefix 3 chars at front
$number = substr($new_code->cd, 3); // get the remaining chars
$new = $number + 1; // add it with 1, php automatically convert strings that can be converted to numbers
$fix_code = $prefix . substr("00000" . $number, -5); // re-assemble the code
}else{
$fix_code = 'CO-00001';
}

Answer 2

you can split the id into two parts, the string one, and the digit one. then increment the digit part then re concat the two parts again
list($strPrefix, $digitPart) = split('-', $oldId);
$digitPart++;
$newCode = $strPrefix . '-' . $digitPart;