mysql左连接不返回来自连接表的行

Question

我有两个相同的表（_impressionsdaily，_impressionsalltime），在每天结束时我将所有数据从日常移动到所有时间。 结构是：ID，purchaseID，印象，唯一，日期。

我运行下面的查询：

SELECT 
    daily.purchaseID, 
    SUM(daily.impression + IFNULL(alltime.impression, 0)) AS impression, 
    SUM(daily.unique + IFNULL(alltime.unique, 0)) AS `unique` 
    FROM _impressionsdaily daily 
    LEFT JOIN _impressionsalltime alltime ON alltime.purchaseID= daily.purchaseID 
    GROUP BY daily.purchaseID; 

的事情是，如果alltime表有不可用在日常采购，我不会看到他们。

基本上这个想法是总结所有的日常和全天候的印象。

---编辑 事情是在每天上午12:00，每天的表被复制到全时，然后删除。 所以给出的解决方案是错误的..

感谢您的帮助， 丹尼

Answer 1

我认为你正在寻找一个Union Select。尝试是这样的：

SELECT DISTINCT(p.ID), p.purchaseID 
FROM (SELECT * 
     FROM _impressionsdaily 
     UNION SELECT * 
     FROM _impressionsalltime) AS p 
GROUP BY p.purchaseID 

Answer 2

SELECT 
daily.purchaseID, 
SUM(daily.impression + IFNULL(alltime.impression, 0)) AS impression, 
SUM(daily.unique + IFNULL(alltime.unique, 0)) AS `unique` 
FROM _impressionsdaily daily 
LEFT JOIN _impressionsalltime alltime ON alltime.purchaseID= daily.purchaseID 
GROUP BY daily.purchaseID; 

在你没有选择任何现场形式_impressionsalltime表这种情况。

您可以使用此SQL从_impressionsalltime表中选择字段以及

SELECT 
alltime.*, 
daily.purchaseID, 
SUM(daily.impression + IFNULL(alltime.impression, 0)) AS impression, 
SUM(daily.unique + IFNULL(alltime.unique, 0)) AS `unique` 
FROM _impressionsdaily daily 
LEFT JOIN _impressionsalltime alltime ON alltime.purchaseID= daily.purchaseID 
GROUP BY daily.purchaseID;