来自 PHP、SQL 查询的奇怪结果

Question

我正在做一个使用数据库的实验，结果很奇怪。

系统是这样的： 我有一个按钮，每次单击它时都会向计数器添加 1。 一旦达到一定数量，就会计算扣分并更新分数

PHP：

$counter = $_POST['counter'];
$user = $_POST['user'];

$sql = "SELECT score FROM board WHERE player = '$user'";
$result = mysqli_query($con,$sql);
$row = mysqli_fetch_array($result);

if($counter == 1)
  $divisor = 0;
else if($counter == 5)
  $divisor = 0.1;
else if($counter == 20)
  $divisor = 0.3;
else if($counter == 50)
  $divisor = 1;}

$deduction = $row['score'] * $divisor;

$sql = "UPDATE board SET score = score - ".$deduction." WHERE player = '$user'";

我从 score = 10 开始 这些就是结果

Score: 10
Counter: 1

Divisor = 0; Deduction = 10 * 0;
UPDATE ... score = score - Deduction (0)
New score = 10
-------------------------------------

Score: 10
Counter: 5

Divisor = 0.1; Deduction = 10 * 0.1;
UPDATE ... score = score - Deduction (1)
New score = 9
-------------------------------------

Score: 9
Counter: 20

Divisor = 0.3; Deduction = 9 * 0.3;
UPDATE ... score = score - Deduction (2.7)
New score = 6.3
-------------------------------------

## Here is the curious part

Score: 6.3
Counter: 50

Divisor = 1; Deduction = 6.3 * 1;
UPDATE ... score = score - Deduction (6.3)
New score = 0.000000190735

知道我为什么会得到 0.000000190735 吗？ 我现在有点迷茫。

B'rgrds，

Answer 1

评论有点长。

这无疑是由score 和$divisor 的不同表示或将$divisor 转换为查询字符串引起的。很难准确指出问题出在哪里，因为有几个不同的地方。

如果确实需要处理，请在数据库中进行计算：

UPDATE board
    SET score = score * (1 - ?)
    WHERE player = ?;

将占位符作为参数传递——而不是修改查询字符串。