function SQL SUM query - php

Question

I have a table with numbers like this:
______________________________________
| 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 |
|_________|__________|______|__________|
Now i want to count them and make a calculation with SUM.
The code i have right now:
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();
}
And i call this function via:
<?php
$count_axle = $database->count_axles($_GET['train_id']);
?>
<?php
foreach($count_axle as $counting){
}
echo $counting['totaldistance'];
?>
Now the output is correct.
(3.2800000000000002) This is the percentage of 25.000
But i want to add 5000 like:
$sql = "SELECT sum(distance)+(5000)/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id";
But when i do that, the output generates something randomly like:
840
Why does it do this, and how do i solve this?

Answer 1

Basic math. You're doing
5000
sum(distance) + --------------
25000 * 100
when you really want
sum(distance) + 5000
------------------------
25000 * 100
Try
SELECT (sum(distance)+(5000))/(25000)*(100)
^--------------------^
instead. Note the extra brackets.
And remember the old BEDMAS mnemonic: brackets, exponents, division, multiplication, addition, subtraction...

Answer 2

Try with:
$sql = "SELECT (sum(distance)+(5000))/(25000)*(100) as totaldistance from axle WHERE train_id = :train_id";
Division has preference over sum operations.