Why does this PDO prepared statement not update the record?

Question

I have a login system and I am currently converting it to PDO, but I think there is something wrong with my code as whenever I run the original code it works and when I run the PDO it doesn't (there are no errors in the console).

This is my original code:

 $update_otp = "UPDATE classadmin SET code = $code, status = $status WHERE code = $fetch_code";
 $update_res = mysqli_query($con, $update_otp);

This is my PDO converted code:

$update_otp  = $conn->prepare("UPDATE classadmin SET code = :code, status = :status WHERE code = :code");
$update_res = $update_otp->execute(['code' => $code, 'status' => $status, 'code' => $fetch_code]);

Answer 1

code occurs twice as a named argument in the given statement, with two different values. This won't work, unless $code === $fetch_code .

---

This might help you out, using distinct names for the named arguments (you are completely free to choose them, they don't need to match the column name):

$update_otp  = $conn->prepare("UPDATE classadmin SET code = :newCode, status = :status WHERE code = :oldCode");
$update_res = $update_otp->execute(['newCode' => $code, 'status' => $status, 'oldCode' => $fetch_code]);

Answer 2

When using emulated prepared statements (this is the default with PDO), the same placeholder can appear multiple times in the SQL. You have :code twice in the SQL. The value that you provide for :code in the execute will be put in place of the two placeholders named :code .

In PHP, associative arrays cannot have the same value with the same key. The one that comes later will overwrite the value with the same key.

$update_otp  = $conn->prepare("
    UPDATE classadmin 
    SET 
      code     = :code, 
      status   = :status 
    WHERE code = :code
");
$update_res = $update_otp->execute([
    'code'   => $code, 
    'status' => $status, 
    'code'   => $fetch_code // <-- This one will overwrite the first $code
]);

To fix the problem use distinctly named placeholders or use positional arguments instead.