Question

我有一张照片排名表。我想根据3列（rating1,2,3）的平均值输出每个类别的前5张照片的ID。

说我有以下表格列（photoID，rating1，rating2，rating3）

 $sth = mysql_query("SELECT * FROM votes ORDER BY AVG(rating1) ASC LIMIT 5") or   die(mysql_error()); 

 $rows = array();
 while($r = mysql_fetch_assoc($sth)) {
 $rows[] = $r;
 }
 echo json_encode($rows);

Answer 1

SELECT rating1+rating2+rating3 AS total FROM `test` ORDER BY total  DESC

此？

Answer 2

默认情况下，MySql中的记录已按升序返回，但您可能希望使用DESC关键字，而不是ASC。如果您尝试选择前5位

，为什么要对ratings1列求平均值？

重新阅读问题，重新提交新答案。

$sth = "SELECT * FROM pics ORDER BY (rating1 + rating2 + rating3) desc LIMIT 5";

Answer 3

您解释问题的方式尚不清楚，这可能是您想要的：

SELECT photoID, AVG((rating1+rating2+rating3)/3) as rating
FROM votes GROUP BY photoID ORDER BY rating DESC LIMIT 5

Answer 4

    SELECT 1            AS category
         , photoID
         , AVG(rating1) AS avg_rating
    FROM votes 
    GROUP BY photoID
    ORDER BY avg_rating DESC 
    LIMIT 5

  UNION ALL

    SELECT 2            AS category
         , photoID
         , AVG(rating2) AS avg_rating
    FROM votes 
    GROUP BY photoID
    ORDER BY avg_rating DESC 
    LIMIT 5

  UNION ALL

    SELECT 3            AS category
         , photoID
         , AVG(rating3) AS avg_rating
    FROM votes 
    GROUP BY photoID
    ORDER BY avg_rating DESC 
    LIMIT 5

php mysql查询前5列的平均值

4 个答案: