How can i generate a unique incremental id like an invoice number (PHP)

Question

Please how can I generate a unique id that increments when a new invoice is created. For example, I have an invoice with the id NR20200001 so the Next invoice created the Id should be NR20200002.

This is my code below, I can't seem to increment the unique id I generated, so I just generated it randomly, but I need to generate it incrementally

<?php 
    $qry = "SELECT * from requisitions order by req_id desc";
    $result = mysqli_query($connection, $qry);
    $row    = mysqli_fetch_array($result);
    $lastid = $row['req_id'];

    if($lastid == ""){
        $number = "NR".date("Y").date("s");
    }
    else{
        $length=2;
        $number = substr($lastid,4);
        $number = intval($number);
        $number = "NR".date("Y").date("s").substr(str_shuffle(str_repeat($x='0123456789',ceil($length/strlen($x)))),1,$length);
    }
?>

Answer 1

Firstly, you should set req_id to primary key and auto increment on database

Secondly, add LIMIT 1 for get only the latest req_id:

$qry = "SELECT * from requisitions order by req_id desc LIMIT 1";

Next, change condition follow as below:

<?php 
$qry = "SELECT * from requisitions order by req_id desc LIMIT 1";
$result = mysqli_query($connection, $qry);
$row    = mysqli_fetch_array($result);

if($row['req_id'] == "" || $row['req_id'] == null)
{
  $lastid = 0;
}
else
{
  $lastid = $row['req_id'];
}

  $nextid = sprintf("%04d", $lastid+1);  //set to 4 digit
  $number = "NR".date("Y").$nextid;

?>

Note: Do not delete record from table because it will make duplicate invoice number. You should add field flag for active/inactive.

Answer 2

Please check code for increment number

6)? $lastid: substr('00000000'. $lastid, -6); $getValue = "NR".date("Y").date("s").$getValue; }?>