Record count for a timeframe

Question

My table employee has a column hiredate of type DATE.
we can see count of records (means how many employees are hired) from that table for a given begin and end hiredate.
Here's the tricky part:
for the timeframe say 03-MAR-2010 to 23-MAR-2010, I want to show results how many people are hired in each week:
resultset should be:
(cutoff date for weeks is Monday midnight: like this)
week no. of employees hired
03-MAR-2010 to 08-MAR-2010(exclusive) 5
08-MAR-2010 to 15-MAR-2010(exclusive) 16
15-MAR-2010 to 22-MAR-2010(exclusive) 67
22-MAR-2010 to 24-MAR-2010(means including employees hired on 23rd) 29
How to do it?

Answer 1

Your solution is great except that is shows the result based on emplyees table not calendar of working days for a concrete period.
For example if nobody was hired for a week then the row for this week will be absent. This info could be useful for diagrams creation.
To address the issue we could join employees on calendar:
select working_days_calendar.start_date,
       working_days_calendar.end_date,
       count(employees.id)
  from ( select distinct
                    min(date_hired) keep (dense_rank first order by date_hired) over (partition by next_day(date_hired, 1)) start_date,
                    max(date_hired) keep (dense_rank last order by date_hired) over (partition by next_day(date_hired, 1)) end_date
             from ( select trunc(to_date('06-APR-10', 'DD-MON-YY')) + level date_hired,
                                to_number(to_char(trunc(to_date('06-APR-10', 'DD-MON-YY')) + level, 'D')) day_of_week
                        from dual
                connect by trunc(to_date('06-APR-10', 'DD-MON-YY')) + level <= trunc(to_date('26-APR-10', 'DD-MON-YY')) )
          where day_of_week between 2 and 6
          order by start_date ) working_days_calendar left join employees on ( employees.hire_date between working_days_calendar.start_date and working_days_calendar.end_date )
group by working_days_calendar.start_date, working_days_calendar.end_dateEdited by: Stepanyan Alexey on 04.04.2010 6:39