php - fetch_assoc() 错误

Question

我收到一条错误，指出第 23 行的 Call to a member function fetch_array() on boolean。第23行由这行代码组成

$row = $query->fetch_assoc();

这是整个区 block

if(!filter_has_var(INPUT_GET, 'id')) {
echo "Error: book id was not found.";
require_once ('includes/footer.php');
exit();
}
$book_id = filter_input(INPUT_GET, 'id', FILTER_SANITIZE_NUMBER_INT);

$sql = "SELECT * FROM books WHERE book_id=" . $book_id;

$query = $conn->query($sql);

$row = $query->fetch_assoc();

Answer 1

添加这个

$query = $conn->query($sql) or trigger_error($mysqli->error."[$sql]");
if ($query->num_rows > 0) {
    while($row = $query->fetch_assoc()) {

    }
} else {
    echo "0 results";
}

Always check for errors when running a query.