GROUP BYの配列

Question

私は複数のskuと価格のデータベースを持っています。 skuあたり約10の価格があります。私がしようとしているのは、以下のスクリプトから平均と中央値を得ることです。

function calculate_median($arr) { 
    sort($arr); 
    $count = count($arr); //total numbers in array 
    $middleval = floor(($count-1)/2); // find the middle value, or the lowest middle value 
    if($count % 2) { // odd number, middle is the median 
     $median = $arr[$middleval]; 
    } else { // even number, calculate avg of 2 medians 
     $low = $arr[$middleval]; 
     $high = $arr[$middleval+1]; 
     $median = (($low+$high)/2); 
    } 
    return $median; 
} 

function calculate_average($arr) { 
    $count = count($arr); //total numbers in array 
    foreach ($arr as $value) { 
     $total = $total + $value; // total value of array numbers 
    } 
    $average = ($total/$count); // get average value 
    return $average; 
} 

$home_values_array = array("100000", "120000", "150000", "157000", "180000", "198000", "220000", "1450000"); 

$median_home_value = calculate_median($home_values_array); 
echo '<p>Median home value: $'.number_format($median_home_value).'<br />'; 
$average_home_value = calculate_average($home_values_array); 
echo 'Average home value: $'.number_format($average_home_value).'</p>'; 

だから私の質問は

$home_values_array = array("100000", "120000", "150000", "157000", "180000", "198000", "220000", "1450000"); 

データベースの例..私はループのうち上記のスクリプトのようにSKUあたりの価格の複数のアレイをできるように、Iグループの特定のSKU行う方法であり、フィールド：ここでは

SKU PRICE 
123 454.60 
123 723.74 
123 523.11 
321 21.00 
321 45.05 

Answer 1

は純粋にSQLアプローチです：

SELECT m.sku, AVG(m.price) as median, MAX(a.price) AS average 
FROM 
(
    SELECT 
     sku 
     , price 
     , (SELECT COUNT(*) FROM prices t2 WHERE t2.sku = t3.sku) AS ct 
     , seq 
     , (SELECT COUNT(*) FROM prices t2 WHERE t2.sku < t3.sku) as delta 
    FROM (
     SELECT 
      sku 
      , price 
      , @rownum := @rownum + 1 AS seq 
     FROM (
      SELECT * FROM prices ORDER BY sku, price 
     ) AS t1, (SELECT @rownum := 0) AS x 
     ORDER BY 
      sku 
      , seq 
    ) AS t3 
    HAVING (ct%2 = 0 AND seq-delta BETWEEN FLOOR((ct+1)/2) AND FLOOR((ct+1)/2) +1) 
     OR (ct%2 <> 0 AND seq-delta = (ct+1)/2) 
) AS m 
INNER JOIN (
    SELECT 
     p.sku 
     ,AVG(p.price) AS price 
    FROM 
     prices AS p 
    GROUP BY sku 
) AS a 
    ON a.sku = m.sku 
GROUP BY sku 
ORDER BY sku; 

中央値計算のためのこの回答の帽子の先端https://dba.stackexchange.com/questions/158333/median-with-group-by