fetch_assoc() loop HTTP ERROR 500 - php

Question

Can't find a way to fetch my results, sql request is good but it keeps crashing (HTTP ERROR 500) when using this code with the while loop.
I don't have any problem when using $row = $result->fetch_assoc(); but I have to loop to update every records.
$sql = "SELECT * FROM reservations WHERE statut = '1' AND NOW() BETWEEN dateAller AND dateRetour"; // requete sql sur les réservations validées dont la tranche horaire est en cours de validité
$result = $conn->query($sql);
if ($result->num_rows > 0) {
while ($row = $result->fetch_assoc()) {
$sql = "UPDATE vehicules SET statut = '2' WHERE immat = '$row[immat]'";
$result = $conn->query($sql);
}
}

Answer 1

you override $result in your Loop, so ->fetch_assoc() will be called on the result of the update Statement in the second iteration. You have to change to:
$sql = "SELECT * FROM reservations WHERE statut = '1' AND NOW() BETWEEN dateAller AND dateRetour"; // requete sql sur les réservations validées dont la tranche horaire est en cours de validité
$result = $conn->query($sql);
if ($result->num_rows > 0) {
while ($row = $result->fetch_assoc()) {
$sql = "UPDATE vehicules SET statut = '2' WHERE immat = '$row[immat]'";
$result2 = $conn->query($sql);
}
}

Answer 2

Change these lines
$sql = "UPDATE vehicules SET statut = '2' WHERE immat = '$row[immat]'";
$result = $conn->query($sql);
to
$sql = "UPDATE vehicules SET statut = '2' WHERE immat = '".$row['immat']."'";
$conn->query($sql);
You are overwriting $result with the result of the update query. You probably don't need this result (at least you are not using it yet), so you can easily remove the assignment.
Additionally you need ' or " to access an array ($row) by a key.
In your case you are lucky and it works without quotes.
Explanation:
PHP sees a constant called immat. If the constant is defined, the value is returned, it isn't defined, PHP falls back to the string "immat".
Anyway it's always a better practice to use quotes!

Answer 3

Try to use this one:
<?php
$sql = "SELECT * FROM reservations WHERE statut = '1' AND NOW() BETWEEN dateAller AND dateRetour";
$result = mysqli_query($conn,$sql);
if (mysqli_num_rows($result) > 0) {
while ($row = mysqli_fetch_assoc($result)) {
$immat = $row["immat"];
$sql = "UPDATE vehicules SET statut = '2' WHERE immat = '$immat'";
$updateResult = mysqli_query($conn,$sql);
}
}
?>