Count in two tables connected with left outer join - mysql

Question

I need a little help with an SQL Query. I want to count number of entries in 2 two tables. my first table called tracking_adspace_views got entry from every view of an Adspace I make. At the end of the day I want to count how much entries I have last day. The second table tracking_clicks count the clicks on a special adspace. So not every adspace which get viewed has clicks. So at the end I want something like
Adspace Id 1 has 500 Views and 3 Clicks
Adspace Id 2 hast 340 Views and 0 Clicks
and so on...
My tables looks like this
tracking_adspace_views
tracking_clicks
My query looks like this:
SELECT '2013-10-31',
views.tracking_adspace,
COUNT(views.tracking_adspace) AS tracking_adspace_views,
COUNT(clicks.tracking_adspace) AS tracking_adspace_clicks
FROM views
LEFT JOIN (
SELECT tracking_adspace,
COUNT(sub_c.tracking_adspace) AS tracking_adspace_clicks
FROM tracking_clicks as sub_c
GROUP BY sub_c.tracking_adspace
) AS clicks
ON clicks.tracking_adspace = views.tracking_adspace
WHERE views.tracking_time LIKE '2013-10-31%'
GROUP BY views.tracking_adspace
That counts the views right and where clicks are 0 are also counted correct. But if there are clicks in click column I get the value from views. Thanks for your help:)
Regards

Answer 1

You appear to be doing a count of a values from rows that will be duplicated by the join.
Try something like this:-
SELECT '2013-10-31' AS TrackingDate,
views.tracking_adspace,
COUNT(views.tracking_adspace) AS tracking_adspace_views,
clicks.tracking_adspace_clicks
FROM views
LEFT JOIN
(
SELECT tracking_adspace,
DATE(tracking_time) AS TrackingDate,
COUNT(tracking_adspace) AS tracking_adspace_clicks
FROM tracking_clicks
GROUP BY tracking_adspace
) AS clicks
ON clicks.tracking_adspace = views.tracking_adspace
AND DATE(views.tracking_time) = clicks.TrackingDate
WHERE DATE(views.tracking_time) = '2013-10-31'
GROUP BY TrackingDate, views.tracking_adspace, clicks.tracking_adspace_clicks

Answer 2

I would expect you to have a third table named tracking_adspaces or something, with a primary key called tracking_adspace. If you do, you could do this:
select '2013-10-13' as TrackingDate,
A.tracking_adspace
V.views,
C.clicks
from tracking_adspaces A
left join (
select tracking_adspace, count(tracking_id) as views
from views
where DATE(tracking_time) = '2013-10-31'
group by tracking_adspace
) V on A.tracking_adspace = V.tracking_adspace
left join (
select tracking_adspace, count(tracking_id) as clicks
from tracking_clicks
where DATE(tracking_time) = '2013-10-31'
group by tracking_adspace
) C on A.tracking_adspace = C.tracking_adspace
If not, you could use
select '2013-10-13' as TrackingDate,
distinct(A.tracking_adspace)
V.views,
C.clicks
from views A
left join (
(etc)