how to write this query using joins? - sql

Question

i have a table campaign which has details of campaign mails sent.
campaign_table: campaign_id campaign_name flag
1 test1 1
2 test2 1
3 test3 0
another table campaign activity which has details of campaign activities.
campaign_activity: campaign_id is_clicked is_opened
1 0 1
1 1 0
2 0 1
2 1 0
I want to get all campaigns with flag value 3 and the number of is_clicked columns with value 1 and number of columns with is_opened value 1 in a single query.
ie. campaign_id campaign_name numberofclicks numberofopens
1 test1 1 1
2 test2 1 1
I did this using sub-query with the query:
select c.campaign_id,c.campaign_name,
(SELECT count(campaign_id) from campaign_activity WHERE campaign_id=c.id AND is_clicked=1) as numberofclicks,
(SELECT count(campaign_id) from campaign_activity WHERE campaign_id=c.id AND is_clicked=1) as numberofopens
FROM
campaign c
WHERE c.flag=1
But people say that using sub-queries are not a good coding convention and you have to use join instead of sub-queries. But i don't know how to get the same result using join. I consulted with some of my colleagues and they are saying that its not possible to use join in this situation. Is it possible to get the same result using joins? if yes, please tell me how.

Answer 1

This should do the trick. Substitute INNER JOIN for LEFT OUTER JOIN if you want to include campaigns which have no activity.
SELECT
c.Campaign_ID
, c.Campaign_Name
, SUM(CASE WHEN a.Is_Clicked = 1 THEN 1 ELSE 0 END) AS NumberOfClicks
, SUM(CASE WHEN a.Is_Opened = 1 THEN 1 ELSE 0 END) AS NumberOfOpens
FROM
dbo.Campaign c
INNER JOIN
dbo.Campaign_Activity a
ON a.Campaign_ID = c.Campaign_ID
GROUP BY
c.Campaign_ID
, c.Campaign_Name

Answer 2

Assuming is_clicked and is_opened are only ever 1 or 0, this should work:
select c.campaign_id, c.campaign_name, sum(d.is_clicked), sum(d.is_opened)
from campaign c inner join campaign_activity d
on c.campaign_id = d.campaign_id
where c.flag = 1
group by c.campaign_id, c.campaign_name
No sub-queries.

Answer 3

Hmm. Is what you want as simple as this? I'm not sure I'm reading the question right...
SELECT
campaign_table.campaign_id, SUM(is_clicked), SUM(is_opened)
FROM
campaign_table
INNER JOIN campaign_activity ON campaign_table.campaign_id = campaign_activity.campaign_id
WHERE
campaign_table.flag = 1
GROUP BY
campaign_table.campaign_id
Note that with an INNER JOIN here, you won't see campaigns where there's nothing corresponding in the campaign_activity table. In that circumstance, you should use a LEFT JOIN, and convert NULL to 0 in the SUM, e.g. SUM(IFNULL(is_clicked, 0)).

Answer 4

I suppose this should do it :
select * from campaign_table inner join campaign_activity on campaign_table.id = campaign_activity.id where campaign_table.flag = 3 and campaign_activity.is_clicked = 1 and campaign_activity.is_opened = 1
Attn : this is not tested in a live situation

Answer 5

The SQL in it's simplest form and most robust form is this: (formatted for readability)
SELECT
campaign_table.campaign_ID, campaign_table.campaign_name, Sum(campaign_activity.is_clicked) AS numberofclicks, Sum(campaign_activity.is_open) AS numberofopens
FROM
campaign_table INNER JOIN campaign_activity ON campaign_table.campaign_ID = campaign_activity.campaign_ID
GROUP BY
campaign_table.campaign_ID, campaign_table.campaign_name, campaign_table.flag
HAVING
campaign_table.flag=1;