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jmhc101
Starting Member

3 Posts
Posted - 01/08/2013 :  12:05:31  Show Profile  Reply with Quote
I have a table of employees with start and end dates. The end date is null if the employee is active. I need to summarise this data to show me the number of active employees at a given point in the month (eg 1st).

Source Data:
employeeID, startDate, endDate
1,20/12/2010,20/03/2011
2,17/01/2011,NULL
3,01/02/2011,20/02/2011

Desired output:
Date, volumeActive
01/01/2011,1
01/02/2011,3
01/03/2011,2

What's the most efficient method of querying this data in TSQL? The source table is large (c.1m records).

nigelrivett
Flowing Fount of Yak Knowledge

United Kingdom
3328 Posts
Posted - 01/08/2013 :  12:13:49  Show Profile  Visit nigelrivett's Homepage  Reply with Quote
select *
from tbl
where d >= startdate and (d < enddate or enddate is null)

then you need the dates

with cte as
(
select d = convert(datetime,20110101')
union all
select d=dateadd(mm,1,d) from cte where d < '20110103'
)
select d, count(*)
from tbl
join cte
on d >= startdate and (d < enddate or enddate is null)
group by d

==========================================
Cursors are useful if you don't know sql.
SSIS can be used in a similar way.
Beer is not cold and it isn't fizzy.
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visakh16
Very Important crosS Applying yaK Herder

India
47051 Posts
Posted - 01/08/2013 :  23:46:06  Show Profile  Reply with Quote
use a calendar table like

http://visakhm.blogspot.in/2010/02/generating-calendar-table.html



then do query like

SELECT f.[Date],t.cnt
FROM dbo,CalendarTable(@StartDate,@EndDate,0,1)f
CROSS APPLY (SELECT COUNT(*) AS cnt
             FROM table
             WHERE f.[Date]>= startDate
             AND (f.[Date] <= endDate OR endDate IS NULL)
             )t


------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/
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jmhc101
Starting Member

3 Posts
Posted - 01/18/2013 :  08:37:10  Show Profile  Reply with Quote
Thanks - both solutions worked and I've learnt something new.
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visakh16
Very Important crosS Applying yaK Herder

India
47051 Posts
Posted - 01/18/2013 :  13:09:58  Show Profile  Reply with Quote
welcome

------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/
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