$result 數量or 長度

$n = mysqli_num_rows($result); // 獲取數據條目數 ->15
$d = mysqli_num_fields($result); // 獲取字段個數 -> 4

↓↓↓↓真相是↓↓↓↓↓(注意：顏色對應着看)

print_r($result);
// -> mysqli_result Object 
( [current_field] => 0 [field_count] => 4 [lengths] => [num_rows] => 15 [type] => 0 )