Php 我的选择产生了什么？

我的

选择有什么问题吗？它应该计算每天不同IP的数量，然后计算总和。以下是查询：

SELECT SUM(NumIpsPerDay) AS user_hits
FROM
  (SELECT DATE(tracking.timestamp) AS DayTrackCount,
          COUNT(DISTINCT tracking.ip) AS NumIpsPerDay
   FROM USER,
        tracking
   GROUP BY DATE(tracking.timestamp)
   WHERE tracking.user_id = $user_id
   GROUP BY $user_id LIMIT 1)

我看着它，我想它可能是日期

我的
选择有什么问题吗？
试试这个：

SELECT SUM(NumIpsPerDay) AS user_hits 
FROM 
(
    SELECT DATE(tracking.timestamp) AS DayTrackCount, 
           COUNT(DISTINCT tracking.ip) AS NumIpsPerDay 
    FROM user, tracking 
    WHERE tracking.user_id = $user_id 
    GROUP BY DATE(tracking.timestamp) 
) x

SELECT SUM(tab.NumIpsPerDay) AS user_hits
FROM
   (SELECT DATE(tracking.timestamp) AS DayTrackCount,
   COUNT(DISTINCT tracking.ip) AS NumIpsPerDay
   FROM USER, tracking
   WHERE tracking.user_id = $user_id
   GROUP BY DATE(tracking.timestamp)) as tab

SELECT SUM(NumIpsPerDay) AS user_hits
FROM (SELECT DATE(tracking.timestamp) AS DayTrackCount,
             COUNT(DISTINCT tracking.ip) AS NumIpsPerDay
      FROM tracking
      WHERE tracking.user_id = $user_id
      GROUP BY DATE(tracking.timestamp
     ) t
GROUP BY $user_id;

为什么要输入子查询日期（tracking.timestamp）？
是的。您正在
用户
和
跟踪
之间进行
交叉联接
（笛卡尔积）。但是，您没有使用
user
表中的任何字段。你可能根本不需要这张桌子

试试这个：

SELECT SUM(tab.NumIpsPerDay) AS user_hits
FROM
   (SELECT DATE(tracking.timestamp) AS DayTrackCount,
   COUNT(DISTINCT tracking.ip) AS NumIpsPerDay
   FROM USER, tracking
   WHERE tracking.user_id = $user_id
   GROUP BY DATE(tracking.timestamp)) as tab

SELECT SUM(NumIpsPerDay) AS user_hits
FROM (SELECT DATE(tracking.timestamp) AS DayTrackCount,
             COUNT(DISTINCT tracking.ip) AS NumIpsPerDay
      FROM tracking
      WHERE tracking.user_id = $user_id
      GROUP BY DATE(tracking.timestamp
     ) t
GROUP BY $user_id;

此外：

子查询没有别名
不需要
限制
where
子句位于
groupby
你为什么会认为有什么不对劲？什么不起作用？你得到了什么结果？你期待什么？你可能想编辑你的问题-你的选择产生了什么吗？如果是这样的话，它做了什么不应该做的？我检查了NumIpsPerDay，没有任何显示。。。所以我不太确定是否正常，在分组之前应该在哪里使用。select有什么问题吗？如果是的话，是什么？