我试图在php L5- 0124-0001中按以下顺序生成我的账单号（其中L5是公司名称，01代表月份，24代表年份，其中最后四位数字是序列号），我从2023年10月开始使用此代码，直到2023年底一切正常，但从今天开始2024年开始，它停止工作，（公司名称正确显示，年月也正确显示，但当需要生成新账单时，最后四位数字不增加。所有账单都保持为0001，而应该是L5-0124-0002等等........以下是代码

$CI = "L5"; //Example only
$CIcnt = strlen($CI);
$offset = $CIcnt + 6;
// Get the current month and year as two-digit strings 
$month = date("m"); // e.g. 09 
$year = date("y"); // e.g. 23  
// Get the last bill number from the database 
$query = "SELECT patientno FROM iap2 ORDER BY patientno DESC LIMIT 1"; 
$result = mysqli_query($con,$query); 
// Use mysqli_fetch_assoc() to get an associative array of the fetched row 
$row = mysqli_fetch_assoc($result); 
// Use $row[‘patientno’] to get the last bill number 
$lastid = $row['patientno'];     
// Check if the last bill number is empty or has a different month or year
if(empty($lastid) || (substr($lastid, $CIcnt + 1, 2) != $month) || (substr($lastid, $CIcnt + 3, 2) != $year)) { 
    // Start a new sequence with 0001 
    $number = "$CI-$month$year-0001"; 
} else { 
    // Increment the last four digits by one 
    $idd = substr($lastid, $offset); // e.g. 0001 
    
    $id = str_pad($idd + 1, 4, 0, STR_PAD_LEFT); // e.g. 0002 
    $number = "$CI-$month$year-$id"; 
}

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