mysql left join doesnt returns rows from joined table

Question

I have 2 identical tables (_impressionsdaily, _impressionsalltime), at the end of every day i move all the data from daily to alltime. The structure is: ID, purchaseID, impression, unique, date.

I run the following query:

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;

The thing is that if the alltime table has purchases that are not available in the daily i wont see them.

Basically the idea is to sum all impressions for both daily and alltime.

---EDIT The thing is at 12:00am everyday the daily table is copied to the alltime and then deleted. so the solution given are wrong..

Thanks for the Help, Danny

Answer 1

I think you're looking for a Union Select . Try something like this:

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;

In this case you haven't selected any field form _impressionsalltime table.

You can use this sql to select field from _impressionsalltime table as well

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;