Question

我想更好地优化我的代码。我希望有一个查询允许别名具有自己的限制，并且还包含无限制的结果。

目前我正在使用两个这样的查询：

// ALL TIME //
$mikep = mysqli_query($link, "SELECT tasks.EID, reports.how_did_gig_go FROM tasks INNER JOIN reports ON tasks.EID=reports.eid WHERE `priority` IS NOT NULL AND `partners_name` IS NOT NULL AND mike IS NOT NULL GROUP BY EID ORDER BY tasks.show_date DESC;"); 
$num_rows_mikep = mysqli_num_rows($mikep);
$rating_sum_mikep = 0;
    while ($row = mysqli_fetch_assoc($mikep)) {
          $rating_mikep = $row['how_did_gig_go'];
          $rating_sum_mikep += $rating_mikep;
    }
$average_mikep = $rating_sum_mikep/$num_rows_mikep;

// AND NOW WITH A LIMIT 10 //

$mikep_limit = mysqli_query($link, "SELECT tasks.EID, reports.how_did_gig_go FROM tasks INNER JOIN reports ON tasks.EID=reports.eid WHERE `priority` IS NOT NULL AND `partners_name` IS NOT NULL AND mike IS NOT NULL GROUP BY EID ORDER BY tasks.show_date DESC LIMIT 10;"); 
$num_rows_mikep_limit = mysqli_num_rows($mikep_limit);
$rating_sum_mikep_limit = 0;
    while ($row = mysqli_fetch_assoc($mikep_limit)) {
          $rating_mikep_limit = $row['how_did_gig_go'];
          $rating_sum_mikep_limit += $rating_mikep_limit;
    }
$average_mikep_limit = $rating_sum_mikep_limit/$num_rows_mikep_limit;

这使我能够显示过去10次评论的历史平均值和平均值。我真的有必要设置两个查询吗？

另外，我知道我可以在查询中得到总和，但并非所有值都是数字，所以我实际上已经用PHP转换它们，但是为了尝试简化显示的内容而省略了代码在代码中。

Answer 1

过去10次评论的历史平均值和平均值

在最佳情况下，您的列how_did_gig_go是100％数字的，像这样的单个查询可以这样工作：

SELECT
      AVG(how_did_gig_go) AS avg_how_did_gig_go
    , SUM(CASE
            WHEN rn <= 10 THEN how_did_gig_go
            ELSE 0 
      END)  / 10              AS latest10_avg
FROM (
      SELECT
            @num + 1 AS rn
          , tasks.show_date
          , reports.how_did_gig_go
      FROM tasks
      INNER JOIN reports ON tasks.EID = reports.eid
      CROSS JOIN ( SELECT @num := 0 AS n ) AS v
      WHERE priority IS NOT NULL
      AND partners_name IS NOT NULL
      AND mike IS NOT NULL
      ORDER BY tasks.show_date DESC
) AS d

但;除非所有“数字”实际上都是数字，否则你注定要从服务器发送每一行以供php处理，除非你能以某种方式清理MySQL中的数据。

如果您为php设置了一个仅使用整个列表中前10位的方法，则可能会避免两次发送所有数据。在PHP中可能有这样做的方法。

如果您希望在SQL中提供帮助，那么可能有2列会有所帮助，这会减少表扫描的数量。

SELECT
      EID
    , how_did_gig_go
    , CASE
            WHEN rn <= 10 THEN how_did_gig_go
            ELSE 0 
      END                AS latest10_how_did_gig_go
FROM (
      SELECT
            @num + 1 AS rn
          , tasks.EID
          , reports.how_did_gig_go
      FROM tasks
      INNER JOIN reports ON tasks.EID = reports.eid
      CROSS JOIN ( SELECT @num := 0 AS n ) AS v
      WHERE priority IS NOT NULL
      AND partners_name IS NOT NULL
      AND mike IS NOT NULL
      ORDER BY tasks.show_date DESC
) AS d

将来（MySQL 8.x）ROW_NUMBER() OVER(order by tasks.show_date DESC)将是比之前显示的“滚动你自己的”行编号（using @num+1）更好的方法。

单个查询，允许别名拥有自己的限制

1 个答案: