not updating

 

This code is just to update the receiptno by adding 1 and displaying the value of receiptno.
The only prob, it does neither.?? says "updated but NOT

 

<?php
$link = mysqli_connect("localhost", "root", "", "homedb"); 
// Check connection
if($link === false){ die("ERROR: Could not connect. " . mysqli_connect_error()); }

$id = 'id';
$receiptno='';

/* Perform a query, check for error */
$sql = "UPDATE control SET 
receiptno = '$receiptno' + 1 where id='$id'";
echo $receiptno;
 if(mysqli_query($link, $sql)){ echo "updated"; } 
else { echo "ERROR: Could not able to execute $sql. " . mysqli_error($link); }
 // Close connection
mysqli_close($link); 
?>

Edited by hamluis, 04 April 2023 - 05:53 PM.
Moved from Web Development to Programming - Hamluis.

You're setting $id to 'id' and $receiptno to an empty string, unless you have a record which has an id of 'id' then SQL query isn't going to update anything at all.