功能SQL SUM查詢

Question

我有數字的表是這樣的：

______________________________________ 
| axle_id | train_id | axle | distance | 
|_________|__________|______|__________| 
| 1  |  1 | 1 | 20 | 
| 2  |  1 | 2 | 50 | 
| 3  |  1 | 3 | 200 | 
| 4  |  1 | 4 | 50 | 
| 5  |  1 | 5 | 200 | 
| 6  |  1 | 6 | 50 | 
| 7  |  1 | 7 | 200 | 
| 8  |  1 | 8 | 50 | 
|_________|__________|______|__________| 

現在我想指望他們，並與SUM計算。 的代碼，我現在：

function count_axles($id) { 
     $sql = "SELECT sum(distance)/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id"; 
     $sth = $this->pdo->prepare($sql); 
     $sth->bindParam(":train_id", $id, PDO::PARAM_STR); 
     $sth->execute(); 
     return $sth->fetchAll(); 
    } 

而且我通過調用這個函數：

<?php 
     $count_axle = $database->count_axles($_GET['train_id']); 
?> 
<?php  
    foreach($count_axle as $counting){ 
    } 

     echo $counting['totaldistance']; 
?> 

現在的輸出是正確的。
（3.2800000000000002）這是25.000
的百分比，但我想補充5000，如：

$sql = "SELECT sum(distance)+(5000)/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id"; 

但是，當我這樣做，輸出隨機生成類似：

爲什麼要這樣做，我該如何解決這個問題？

Answer 1

基本數學。你做

     5000 
    sum(distance) + -------------- 
        25000 * 100 

當你真的想

sum(distance) + 5000 
    ------------------------ 
     25000 * 100 

嘗試

SELECT (sum(distance)+(5000))/(25000)*(100) 
     ^--------------------^ 

代替。請注意額外的括號。

記住老BEDMAS助記符：括號，指數，除法，乘法，加法，減法...

Answer 2

嘗試用：

$sql = "SELECT (sum(distance)+(5000))/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id"; 

司擁有和操作偏好。