Is this possible with mysql?

Question

First of all: sorry for the title, but maybe I will find a better one later.

I asked this some minutes ago, but since I was not able to describe what I want I try it

Answer 1

Another Update: Accidently (by copy&paste) had starttime = ... or starttime = ... but it should be starttime = ... or endtime = ...

UPDATE:

To explain my query in more detail (in the final query there are even more comments):

First we simply got

SELECT
...
FROM gc_sessions s
WHERE DATE(starttime) = CURDATE() OR DATE(endtime) = CURDATE()

That's nothing more like saying "give me all users whose session started today or ended today". Having to consider those two times again and again makes the query a bit clumsy, but actually it's not that complicated.

So, usually we would use the COUNT() function to count something, obviously, but since we want "conditional counting", we simply use the SUM() function and tell it when to add 1 and when not.

SUM (CASE WHEN ... THEN 1 ELSE 0 END) AS a_column_name

The SUM() function examines now each row in the result set of sessions from today. So for each user in this result set we look if this user was online the date we specify. It doesn't matter how many times he/she was online, so for performance reasons we use EXISTS. With EXISTS you can specify a subquery which stops as soon as something is found, so it doesn't matter what it returns when something is found, as long as it's not NULL. So don't get confused why I selected 1. In the subquery we have to connect the user which is currently examined from the outer query with the user from the inner query (subquery) and specify the time window. If all criterias meet count 1 else 0 like explained before.

SUM(CASE WHEN 
         EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                  AND ((date(starttime) = CURDATE() - INTERVAL 1 DAY) 
                       OR (date(endtime) = CURDATE() - INTERVAL 1 DAY))) 
    THEN 1 ELSE 0 END) AS todayAndYesterday,

Then we make a column for each condition and voila, you have all you need in one query. So with your updated question your criteria has changed, we just have to add more rules:

SELECT
/*this is like before*/
SUM(CASE WHEN 
         EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                  AND ((date(starttime) = CURDATE() - INTERVAL 1 DAY) 
                       OR (date(endtime) = CURDATE() - INTERVAL 1 DAY))) 
    THEN 1 ELSE 0 END) AS FridayAndThursday,
SUM(CASE WHEN 
         EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                  AND ((date(starttime) = CURDATE() - INTERVAL 2 DAY) 
                       OR (date(endtime) = CURDATE() - INTERVAL 2 DAY)))
         /*this one here is a new addition, since you don't want to count the users that were online yesterday*/
         AND NOT EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                  AND ((date(starttime) = CURDATE() - INTERVAL 1 DAY) 
                       OR (date(endtime) = CURDATE() - INTERVAL 1 DAY)))
    THEN 1 ELSE 0 END) AS FridayAndWednesdayButNotThursday,
SUM(CASE WHEN 
         EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                  AND ((date(starttime) = CURDATE() - INTERVAL 3 DAY) /* minus 3 days to get tuesday*/
                       OR (date(endtime) = CURDATE() - INTERVAL 3 DAY)))
         /*this is the same as before, we check again that the user was not online between today and tuesday, but this time we really use BETWEEN for convenience*/
         AND NOT EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                  AND ((date(starttime) BETWEEN CURDATE() - INTERVAL 2 DAY AND CURDATE() - INTERVAL 1 DAY) 
                       OR (date(endtime) BETWEEN CURDATE() - INTERVAL 2 DAY AND CURDATE() - INTERVAL 1 DAY)))
    THEN 1 ELSE 0 END) AS FridayAndTuesdayButNotThursdayAndNotWednesday,
.../*and so on*/
FROM gc_sessions s
WHERE DATE(starttime) = CURDATE() OR DATE(endtime) = CURDATE()

So, I hope you get the idea now. Any more questions? Feel free to ask.

end of update

Answer to previous version of question:

select 
SUM(CASE WHEN EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                      AND ((date(starttime) = CURDATE() - INTERVAL 1 DAY) 
                           OR (date(starttime) = CURDATE() - INTERVAL 1 DAY))) 
    THEN 1 ELSE 0 END) AS todayAndYesterday,
SUM(CASE WHEN EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                      AND ((date(starttime) BETWEEN CURDATE() - INTERVAL 2 DAY AND CURDATE() - INTERVAL 1 DAY) 
                           OR (date(starttime) BETWEEN CURDATE() - INTERVAL 2 DAY AND CURDATE() - INTERVAL 1 DAY))) 
    THEN 1 ELSE 0 END) AS todayAndYesterdayOrTheDayBeforeYesterday,
SUM(CASE WHEN EXISTS (SELECT 1 FROM gc_sessions sub_s WHERE s.user = sub_s.user 
                      AND ((date(starttime) BETWEEN CURDATE() - INTERVAL 7 DAY AND CURDATE() - INTERVAL 1 DAY) 
                           OR (date(starttime) BETWEEN CURDATE() - INTERVAL 7 DAY AND CURDATE() - INTERVAL 1 DAY))) 
    THEN 1 ELSE 0 END) AS todayAndWithinTheLastWeek
from gc_sessions s
where date(starttime) = CURDATE()
or date(endtime) = CURDATE()