table1 - Calendar - Календарь дат с 2014 по 2018 гг
tDate    dateid
29.01.2015       5
30.01.2015       6
31.01.2015       7

table2 - Summary
Logdate    ComputerID
29.01.2015       56
31.01.2015       56

Logdate    ComputerID
29.01.2015       56
30.01.2015       56 
31.01.2015       56

select
we_Calendar.tDate,
we_SummaryActivities.ComputerId
        from we_Calendar
        INNER JOIN we_SummaryActivities ON we_SummaryActivities.LogDate=we_Calendar.tDate
        where we_Calendar.tDate NOT IN
        (SELECT we_SummaryActivities.LogDate
from we_SummaryActivities
GROUP BY we_SummaryActivities.LogDate,we_SummaryActivities.ComputerId)

select
 b.tDate, a.ComputerID
from
 (select distinct ComputerID from we_SummaryActivities) a cross join
 we_Calendar b
where
 not exists(select 1 from we_SummaryActivities where ComputerID = a.ComputerID and LogDate = b.tDate);

and b.tDate >= (select min(LogDate) from we_SummaryActivities where ComputerID = ...)

and b.tDate >= (select min(LogDate) from we_SummaryActivities where ComputerID = s.ComputerID)