如何使用PHP增加唯一的收据编号并在mysql数据库中更新它？

Question

I am trying to increment a receipt number and add that new receipt number in the mysql database.

Here is my code that i have written:

<?php 
    require 'config.php';
    $sql = "SELECT * FROM receipts ORDER BY id";
    $result = $conn->query($sql);
    $row = $result->fetch_assoc();
    $date = date("ymdhs");
    $row2 = $row['id'];
    $recnum = $date.'-00'.($row2+);
    echo $recnum ;
    $sql = "UPDATE receipts SET recnum='$recnum' WHERE id='$row2'";
    if ($conn->query($sql) === TRUE) {
        echo "updated";
    } else {
        echo "Error updating record: " . $conn->error;
    }

    $conn->close();

?>

Answer 1

The order is not specified in your select query. Thus, you get no guarantees from your RDBMS that your data will come back in a certain order - or even in a consistent order - unless you query your data with an ORDER BY clause. If you want to rely on this order, you must specify your desired order using ORDER BY. "$row2+" wont increment $row2, use (++$row2) - plus plus should be before the variable- instead.

Answer 2

I have managed to debug my code. here is the working code.

<?php 

    require 'config.php';
        $sql = "SELECT * FROM receipts ORDER BY id DESC LIMIT 1";
    $result = $conn->query($sql);
    $row = $result->fetch_assoc();
    $date = date("ymdhs");
    $row2 = $row['id'];
    $recnum = $date.'-00'.$row2;
    echo $recnum ;
    $sql = "UPDATE receipts SET recnum='$recnum' WHERE id='$row2'";
    if ($conn->query($sql) === TRUE) {
        echo "";
    } else {
        echo "Error updating record: " . $conn->error;
    }

    $conn->close();

?>