PHP mysqli_fetch_array应该得到一个布尔值

Question

$result = mysqli_query($conn,"SELECT * FROM Players");
if ($result !== FALSE) {
    while($row = mysqli_fetch_array($result)) {
        $result = mysqli_query($conn,"UPDATE Players SET Score='$score' WHERE ID='$id'");
    }
}

This works. That is, the databse is indeed updated and everything is all cool.

But it throws a warning:

Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given

If you search around, the explanation is that the query is failing - hence, it is returning FALSE, so you get the warning.

... But this doesn't make sense in my case. The query is not failing. When I run this script, my database is updated just fine. Besides, there is also a conditional checking if the result is a boolean before using mysqli_fetch_array, so technically this warning should never happen in the first place.

Whatever, the problem must be with $result. Let's do:

echo gettype($result);

Which results in

"object"

Well, this explains why is it passing the condition. However, this still won't explain why mysqli_fetch_array insists this is a boolean (because it isn't).

What is the problem, then?

Tested with PHP Version 5.3.24 and 5.4.19.

Answer 1

You're overwriting the resultset $result from your SELECT query with a new $result value from the UPDATE query inside your loop

while($row = mysqli_fetch_array($result)) {
    $result2 = mysqli_query($conn,"UPDATE Players SET Score='$score' WHERE ID='$id'");
}