mysql左連接不返回來自連接表的行

Question

我有兩個相同的表（_impressionsdaily，_impressionsalltime），在每天結束時我將所有數據從日常移動到所有時間。 結構是：ID，purchaseID，印象，唯一，日期。

我運行下面的查詢：

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表有不可用在日常採購，我不會看到他們。

基本上這個想法是總結所有的日常和全天候的印象。

---編輯 事情是在每天上午12:00，每天的表被複制到全時，然後刪除。 所以給出的解決方案是錯誤的..

感謝您的幫助， 丹尼

Answer 1

我認爲你正在尋找一個Union Select。嘗試是這樣的：

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; 

在你沒有選擇任何現場形式_impressionsalltime表這種情況。

您可以使用此SQL從_impressionsalltime表中選擇字段以及

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;