我的桌子上有这样的数字:
______________________________________
| 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 |
|_________|__________|______|__________|
现在我想计算它们并用SUM进行计算。 我现在的代码:
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();
}
我通过以下方式调用此函数:
<?php
$count_axle = $database->count_axles($_GET['train_id']);
?>
<?php
foreach($count_axle as $counting){
}
echo $counting['totaldistance'];
?>
现在输出正确。
(3.2800000000000002)这是25.000的百分比
但我想添加5000像:
$sql = "SELECT sum(distance)+(5000)/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id";
但是当我这样做时,输出产生一些随机的东西,如: 840
为什么会这样做,我该如何解决这个问题?
答案 0 :(得分:6)
基础数学。你在做什么
5000
sum(distance) + --------------
25000 * 100
当你真的想要
时 sum(distance) + 5000
------------------------
25000 * 100
尝试
SELECT (sum(distance)+(5000))/(25000)*(100)
^--------------------^
代替。注意额外的括号。
记住旧的BEDMAS助记符:括号,指数,除法,乘法,加法,减法......
答案 1 :(得分:1)
尝试:
$sql = "SELECT (sum(distance)+(5000))/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id";
分部优先于总和操作。