Get last number from unique ID from database SQL - PHP CodeIgniter - php

Question

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I have Registration table like this:
table
Now I'm hopping to get the last digit, for example:
SG20160412001 >> 1
SG20160412056 >> 56
SG20160412121 >> 121
The purpose is for generating new Reg_ID, for example:
If the returned data is = 1 then the new Reg_ID will be SG20160412002
If the returned data is = 56 then the new Reg_ID will be SG20160412057
If the returned data is = 0 then the new reg_ID will be SG20160412001
Here's my current code:
public function generate_no_reg($nmNegara)
{
$dtNow = date('Y-m-d');
$query = 'SELECT COUNT(Reg)ID) FROM Registratrion WHERE Reg_Date="$dtNow"';
$lastid = $this->db->query($query);
$id = $lastid->num_rows()+1;
$regCount = format_no_registrasi($id);
$kode = $this->get_negara($nmNegara).$regCount;
return $kode;
}
And here's my current code for generating the last 3 digit:
function format_no_registrasi($no)
{
$leadingzeros = '000';
$no_reg = date('Y') . date('m') . substr($leadingzeros, 0, (-strlen($no))) . $no+1;
return $no_reg;
}
The problem I'm having from this code is:
When i delete a row, the Primary Key will be doubled, example:
SG20160412001 << I delete this one
SG20160412002
Now the data count is returning 1, and when I generate new one it will be: SG20160412002
Any help is very much appreciated. Sorry for the problem.
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Answer 1

This query cuts 3 last signs from Reg_ID and returns max value.
select max(cast(substr(Reg_ID, -3) as UNSIGNED))
from FROM Registratrion
WHERE Reg_Date="$dtNow"
So id numeration supports ids till 999

Answer 2

Max' solution is much cleaner.
Don't use the count, use the highest number.
Create the leading characters of the Reg_ID
$leadingCharacters = 'SG' + date('Ymd');
Then select the hightes Reg_ID that starts with this string:
select Reg_ID from Registration where Reg_ID like '$leadingCharacters%' order by Reg_ID desc limit 0,1
Then extract the last three digits from the result, convert it to int and increment it. This will be your next ID.
$number = (int) substr($result,-3);
$number++;
NOTICE: Typed the code from memory, so there might be a little error in it. But the concept should work though

Answer 3

Have you considered splitting out your reg_id into three columns?
prefix CHAR(2)
reg_date DATE
postfix SMALLINT UNSIGNED
You can use a surrogate or composite PRIMARY if you need and concat the columns on select:
SELECT CONCAT(prefix, reg_date, LPAD(post_fix,3,'0')) reg_id
FROM registration
Keeping separate data in separate fields saves a lot of headache with operations like this.

Answer 4

My answer is helped by Markus and Max
This is the function that i used for leading characters, since the 'SG' is from database:
public function get_negara($nmNegara)
{
$this->db->select('Kode_Negara');
$this->db->from('tb_negara_tujuan');
$this->db->where('Nama_Negara',$nmNegara);
$query = $this->db->get();
$result = $query->row();
return $result->Kode_Negara . date('Ymd');
}
// this will returning 'SG20160413'
This is the helper function used to convert 1 to 001:
function format_no_registrasi($no)
{
$leadingzeros = '000';
$no_reg = substr($leadingzeros, 0, (-strlen($no))) . $no;
return $no_reg;
}
This is the function used to generate the full Reg_ID:
public function generate_no_reg($nmNegara)
{
$leadingChar = $this->get_negara($nmNegara);
$this->db->select_max('No_Registrasi');
$this->db->like('No_Registrasi',$leadingChar);
$query = $this->db->get('tb_registrasi');
$result = $query->row();
$noreg = (int) substr($result->No_Registrasi,-3);
$noreg++;
return $kode = $leadingChar.format_no_registrasi($noreg);
}