Using transactions for queries which have dependant results - php

Question

Here is my script structure:
try {
$dbh_conn->beginTransaction();
$stmt1 = $dbh_conn->prepare("SELECT user_id FROM activate_account WHERE token = ?");
$stmt1->execute(array($validate_activate_token));
$num_rows = $stmt1->fetch(PDO::FETCH_ASSOC);
if($num_rows) {
$user_id = $num_rows['user_id'];
$stmt2 = $dbh_conn->prepare("UPDATE users SET active = 1 WHERE id = ?");
$stmt2->execute(array($user_id));
$updated = $stmt2->rowCount();
if ( $updated > 0 ){
$stmt3 = $dbh_conn->prepare("DELETE FROM activate_account WHERE token = ?");
$stmt3->execute(array($validate_activate_token));
$status = "all fine";
} else {
$status = "first problem";
}
} else {
$status = "second problem";
}
$dbh_conn->commit();
echo $status;
die;
} catch(PDOException $e) {
$dbh_conn->rollBack();
$status = "third problem";
echo $status;
die;
}
The result of my code always is second problem. Why? And how can I rewrite my code to fix it?
Note that I've tested this condition if($num_rows) { separately (in another script singly) and it is true, but when I write it into script above, it is always false.

Answer 1

The purpose of transactions is to make sure that queries that must happen together are never broken up. In your use case, the first query can be executed in isolation with no downside.
Put the last two in a transaction, but leave the first alone. If the first fails, just don't run the other two.
If the first succeeds but one of the other two (in the transaction) fails so that neither of the two is committed, you're no worse off for having executed the first.