貝葉斯算法返回0

Question

我試圖通過MySQL和PHP在上週獲得最高評價的照片。我發現貝葉斯公式可能是我需要的，但我一直在搞這個無濟於事。

以下代碼不返回任何錯誤，它只返回單個'0'。爲什麼這是我沒有絲毫的。

$bayesian_algo = "SELECT 
      photo_id, 
      (SELECT count(photo_id) FROM photo_ratings)/
(SELECT count(DISTINCT photo_id) FROM photo_ratings) AS avg_num_votes, 
      (SELECT avg(rating) FROM photo_ratings) AS avg_rating, 
      count(photo_id) as this_num_votes, 
      avg(rating) as this_rating 
      FROM photo_ratings 
      WHERE `date` > '$timeframe' 
      GROUP BY photo_id"; 

$bayesian_info = $mysqli->query($bayesian_algo); 

$all_bayesian_info = array(); 
while($row=$bayesian_info->fetch_assoc()) array_push($all_bayesian_info,$row); 

list($photo_id,$avg_num_votes,$avg_rating,$this_num_votes,$this_rating) = $all_bayesian_info; 
$photo_id = intval($photo_id); 
$avg_num_votes = intval($avg_num_votes); 
$avg_rating = intval($avg_rating); 
$this_num_votes = intval($this_num_votes); 
$this_rating = intval($this_rating); 

$bayesian_result = (($avg_num_votes * $avg_rating) + ($this_num_votes * $this_rating))/($avg_num_votes + $this_num_votes); 

echo $bayesian_result; // 0?? 

我的數據庫看起來是這樣的：

photo_id | user_id | rating | date 

所有字段存儲爲int（我存儲日期作爲UNIX時間戳）。

我累了，硬拼編碼，通常我至少可以得到一個遠一點，如果有錯誤信息（或任何東西！），但沒有辦法，我得到的數據，如果我var_dump($all_bayesian_info)將永遠返回0

Answer 1

讓我們在mysql查詢本身中做複雜的貝葉斯計算！

的代碼可以寫成這樣：

$bayesian_algo_result = "SELECT *, 
(((resultdata.avg_num_votes * resultdata.avg_rating) + (resultdata.this_num_votes * resultdata.this_rating))/(resultdata.avg_num_votes + resultdata.this_num_votes)) AS bayesian_result 
FROM 
( 
SELECT 
    photo_id, 
    (SELECT count(photo_id) FROM photo_ratings)/
     (SELECT count(DISTINCT photo_id) FROM photo_ratings) AS avg_num_votes, 
    (SELECT avg(rating) FROM photo_ratings) AS avg_rating, 
    count(photo_id) as this_num_votes, 
    avg(rating) as this_rating  
FROM photo_ratings 
WHERE `date` > '$timeframe' 
GROUP BY photo_id 
) AS resultdata; 
"; 

$bayesian_result_info = $mysqli->query($bayesian_algo_result); 

//loop through the rows. 
while($row = $bayesian_result_info->fetch_assoc()) { 
    list(
     $photo_id, 
     $avg_num_votes, 
     $avg_rating, 
     $this_num_votes, 
     $this_rating, 
     $bayesian_result 
    ) = $row; 

    echo 'Balesian rating for photo' . $photo_id . ' is: ' . $bayesian_result; 
} 

注：

• 這裏是一個工作的SQL小提琴：http://sqlfiddle.com/#!2/d4a71/1/0

• 我因此未作任何邏輯改變你公式。所以請確保你的公式是正確的。

• 如果/當UNIX時間戳轉爲64位數據類型，那麼您將不得不使用MySQL「bigint」來存儲它們（用於'日期'列）。