Question

<?php 
        $new_result = mysqli_query($con, "SELECT input_cost FROM data_input");
        while ($new = mysqli_fetch_array($new_result)) {

            $sum += $new['input_cost'];
        }

        echo "<h2> total cost of this month is $".$sum. "</h2>";

     ?>

但结果说

<br>

注意：未定义的变量：总和 C：\ xampp \ htdocs \ work_shop \ back_end \ data_input_output \ result.php on 第57行

<br>

本月总费用为$300 这是正确的结果......

<br>

我该如何解决这个问题...... ??

Answer 1

$ sum未定义，因为您只是添加，而不是设置值。

<?php 
  $new_result = mysqli_query($con, "SELECT input_cost FROM data_input");
  $sum = 0;
  while ($new = mysqli_fetch_array($new_result)) {
    $sum += $new['input_cost'];
  }
  echo '<h2> total cost of this month is $'.$sum.'</h2>';
?>

Answer 2

您需要在外部循环中定义$sum变量。试试这个 -

<?php 


$sum = 0; // define sum outside loop

$new_result = mysqli_query($con, "SELECT input_cost FROM data_input");
while ($new = mysqli_fetch_array($new_result)) {

     $sum += $new['input_cost'];
}

 echo "<h2> total cost of this month is $".$sum. "</h2>";

?>

如何将mysql数值数据与另一个mysql数值数据相加

2 个答案: