How to use sub query in group by clause sql server 2005 - sql-server-2005

Question

my table data as follows
FinishDate SpecialistName jobstate
----------------------- --------------- ---------
2012-10-01 00:00:00.000 Josh FINISHED
2012-10-01 00:00:00.000 Josh FINISHED
2012-10-01 00:00:00.000 Sam FINISHED
2012-10-01 00:00:00.000 Robin FINISHED
2012-10-01 00:00:00.000 Robin FINISHED
2012-10-01 00:00:00.000 Joy FINISHED
2012-10-01 00:00:00.000 Joy INCOMMING
2012-10-02 00:00:00.000 Joy FINISHED
my query as follows
select Count(*) [Count] from employee
where convert(varchar,FinishDate,112)>='20121001'
and convert(varchar,FinishDate,112) <='20121001'
and JobState='FINISHED'
group by SpecialistName
if a particular specialist finish multiple jobs in same day then i want to show 1
if robin,josh & Sam finish 10 jobs in same day then 3 will be shown for that day
then output will be like
FinishDate Count
----------------------- ------
2012-10-01 00:00:00.000 3
2012-10-02 00:00:00.000 5
2012-10-03 00:00:00.000 15
so just guide me how to customize my sql to have desire result. thanks

Answer 1

try something along these lines. Syntax may not be perfect (did "freehand")
Select
TheDate
, Count(*) [Count]
From
(
select
convert(varchar,FinishDate,112) TheDate
, SpecialistName
from employee
where convert(varchar,FinishDate,112)>='20121001'
and convert(varchar,FinishDate,112) <='20121001'
and JobState='FINISHED'
group by
convert(varchar,FinishDate,112)
, SpecialistName
) t1
Group By
TheDate
It has to be two selects because the groupings that you want are different. If you did a single select grouping by FinishDate and SpecialistName what you would get would be a count of the distinct combinations of those two.
What you want is to get the distinct SpecialistNames that had at least one entry in a date. Distinct because you care that they had an entry, but not whether they had 1 or 3 or 17. This is done by the inner query.
Then you want to take these distinct SpecialistName with corresponding date and summarize them by FinishDate to get a count of specialists by date. This is done by the outer query.
Part of your comment mentions Distinct and you could in fact use Select Distinct instead of Group By in the inner query since we don’t need a count there. The outer query does require the Group By since you do need a count. My own bias is to use group by rather than distinct in case I need an aggregate function later, but that’s me. It would be perfectly OK to use Select Distinct if you prefer.