fetch_assoc（）错误

Question

我收到的错误是在第23行的boolean上调用成员函数fetch_array（）。 第23行由这行代码组成

$row = $query->fetch_assoc();

这是整个块

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

添加此

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

    }
} else {
    echo "0 results";
}

  

运行查询时始终检查错误。