New SQL PDO query from result - php

Question

I'm very new to PDO SQL queries. I have the following code which works well. When the result returns only 1 row, I then want to set that row to valid = FALSE". How do I do that?
$sql = "SELECT * FROM `passcodes` WHERE `passcode` = '$passcode' AND `valid` = TRUE";
$stmt = $DBcon->prepare($sql);
$stmt->execute();
$count = $stmt->rowCount();
if($count == 1) {
//do this
} else {
//do that
}

Answer 1

Yet another solution.
IF you interested in "else" section mentioned above, you can combine elegant solution from #YourCommonSense with checking how much rows was changed in UPDATE. MySQL returns such info!
$sql = "UPDATE `passcodes` SET `valid` = FALSE WHERE `passcode` = ? AND `valid` = TRUE";
$DBcon->prepare($sql)->execute([$passcode]);
if ($stmt->rowCount() == 0) {
// do this when nothing found
}

Answer 2

I then want to set that row to valid = FALSE". How do I do that?
this is what SQL is for.
$sql = "UPDATE `passcodes` SET `valid` = FALSE WHERE `passcode` = ? AND `valid` = TRUE";
$DBcon->prepare($sql)->execute([$passcode]);
this is all the code you need.

Answer 3

This will work with count of result rows equal or greater than 1.
I recommend to use placeholders for prepared statements:
$sql = "SELECT `id` FROM `passcodes` WHERE `passcode` = ? AND `valid` = TRUE";
$stmt = $DBcon->prepare($sql);
$stmt->execute([ $passcode ]);
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
if($rows) {
//do this
$sql = "UPDATE `passcodes` SET `valid` = FALSE WHERE `id` = ?";
$stmt = $DBcon->prepare($sql);
foreach ($rows as $r) {
$stmt->execute([ $r['id'] ]);
}
} else {
//do that
}