计算过去 30 天的平均燃料

Question

我有一个脚本可以计算过去 30 天的平均油耗，但一些用户报告计算错误。

这就是我所拥有的：

//Calculate the total km for the last 30 days
    $result = mysqli_query($con,"SELECT MIN(km) AS minikm, MAX(km) AS maxkm FROM diesel WHERE diesel.dato >= '$dx' AND userid = ".$_COOKIE['userid']." ORDER BY diesel.dato DESC");
    while($row = mysqli_fetch_array($result)){ $mileage = $row['maxkm'] - $row['minikm'];}

//Sum up all the Liters of diesel
    $result = mysqli_query($con,"SELECT SUM(liter) AS totalfuel FROM diesel WHERE diesel.dato >= '$dx' AND userid = ".$_COOKIE['userid']." ORDER BY diesel.dato DESC");
    while($row = mysqli_fetch_array($result)){ $totalfuel = $row['totalfuel'];} 

$averagefuel = $totalfuel / $mileage * 10;

在解决此问题时，我注意到我不应该在计算的第一条记录中包含升。只有总公里数。那么我该怎么做呢？

Answer 1

如果我必须推测用户的想法，问题是一个月的燃料输入与当月的燃料消耗有些无关。换句话说，水箱可能开始空满或介于两者之间。而且，它可能会以空、满或介于两者之间的方式结束。

这意味着您的计算可能会在任一侧最多加满油箱。

现在，这可能会因特定情况而得到缓解。例如，也许这些车辆每天都在行驶，他们的油箱在一天结束时被加满。因此，在午夜，您可以合理地假设水箱已满。如果是这种情况，我会感到惊讶，因为汽车中的燃料库存需要花钱。他们可以聘请我作为顾问来改善他们的资产负债表；）（仅作记录，这不是我的专长）。

作为一个小提示，您可以在 SQL 中进行完整的计算。您不需要使用两个查询或任何客户端计算：

SELECT 10 * SUM(liter) / (MAX(km) - MIN(km)) as AvgFuel
FROM diesel
WHERE diesel.dato >= '$dx' AND userid = ".$_COOKIE['userid'].";

Answer 2

我认为您需要一直添加 $mileage。试试这个：

//Calculate the total km for the last 30 days
$mileage = 0;
    $result = mysqli_query($con,"SELECT MIN(km) AS minikm, MAX(km) AS maxkm FROM diesel WHERE diesel.dato >= '$dx' AND userid = ".$_COOKIE['userid']." ORDER BY diesel.dato DESC");
    while($row = mysqli_fetch_array($result)){ $mileage += $row['maxkm'] - $row['minikm'];}

//Sum up all the Liters of diesel
    $result = mysqli_query($con,"SELECT SUM(liter) AS totalfuel FROM diesel WHERE diesel.dato >= '$dx' AND userid = ".$_COOKIE['userid']." ORDER BY diesel.dato DESC");
    while($row = mysqli_fetch_array($result)){ $totalfuel = $row['totalfuel'];} 

$averagefuel = $totalfuel / $mileage * 10;

Gordon Linoff 为您提供了很好的解决方案。尝试使用这个：

//Calculate the total km for the last 30 days
$mileage = 0;
$result = mysqli_query($con,
"SELECT 10 * SUM(liter) / (MAX(km) - MIN(km)) as AvgFuel
FROM diesel
WHERE diesel.dato >= '$dx' AND userid = ".$_COOKIE['userid']);
$averagefuel = $steps = 0; 
while($row = mysqli_fetch_array($result)){ 
    $averagefuel += $row['AvgFuel']; 
    $steps++; 
} 
$averagefuel = $averagefuel/$steps;