Auto generate invoice number in php with financial year format?

How to create auto generated invoice number in  PHP with financial year format?

Here I am going to share one of my work to generate auto Invoice number in PHP along with current financial year just like 18-19/0000001, 18-19/0000002.

<?php

function invoiceId()

{

$db=getDB();

$max = $db->prepare("select max(id) mid from invoice_table");

$max->execute();

$row = $max->fetch(PDO::FETCH_BOTH);

$mid= $row['mid']+1;

$y=date('y');

$m=date('m');

$cy;

$ny;

if($m<4)

{

$cy=$y-1;

$ny=$y;

}

else

{

$cy=$y;

$ny=$y+1;

}

 $id =$cy."-".$ny."/".str_pad($mid, 8, "0", STR_PAD_LEFT);

 return $id;

}

?>

just call this function while inserting record it will return id.