PHP 从 mysql 中提取每日平均值的平均值

Question

我正在使用 mysql 计算表中的每日平均花费。在 php 中，我想将所有这些日平均值平均为 1 个日平均值。最终，我想对多个表执行此操作，并在高图表中绘制最终平均值。现在，我无法让 php 平均查询结果。我正在连接到我的数据库，但只是没有在代码中显示它。请参阅下面的代码:

<?php

    function array_average($arr){
        $sum = array_sum($arr);
        $num = sizeof($arr);
        echo $sum/$num;
    }

    $sth = mysql_query("SELECT round((sum(d_power),2) as $perton FROM pheom.pheom_gb WHERE timestamp between subdate(curdate(), interval 3 month) and curdate() GROUP BY Day(timestamp) ORDER BY Timestamp");
    $rows = array();
    while($r = mysql_fetch_array($sth)) {
        $rows['data'][] = $r['$perton'];
    }

    echo array_average($rows);

    mysql_close($con);
?>

Answer 1

为什么不用SQL来计算呢？

select avg($perton) as $perton
from (SELECT round(sum(d_power), 2) as $perton
      FROM pheom.pheom_gb
      WHERE timestamp between subdate(curdate(), interval 3 month) and curdate()
      GROUP BY Day(timestamp)
     ) t;