Calculate number of concurrent events in SQL

Question

I have a table that holds phone calls, with the following fields:

• ID
• STARTTIME
• ENDTIME
• STATUS
• CALL_FROM
• CALL_TO

Answer 1

Try this in lieu of your between and a cross join:

select
    t1.sid,
    count(1) as CountSimultaneous
from
   calls_nov t1
   inner join nov t2 on
       t1.starttime <= t2.endtime
       and t1.endtime >= t2.starttime
where
    t1.starttime between '2011-11-02' and '2011-11-03'
group by
    t1.sid
order by CountSimultaneous desc