SQL query for getting active employees in specific period - sql

Question

Having the following table:
ID EmployeeID Status EffectiveDate
------------------------------------------------------
1 110545 Active 01AUG2011
2 110700 Active 05JAN2012
3 110060 Active 05JAN2012
4 110222 Active 30JUN2012
5 110545 Resigned 01JUL2012
6 110545 Active 12FEB2013
How do I get the number of active (or partially active) in a specific period?
For example, if I want to know all active (or partially active) employees from 01JAN2011 to 01AUG2012 I should get 4 (according to the table above). If I want to know all active employees from 01AUG2012 to 01JAN2013 it should be 3 only (because employee 110454 is resigned).
How will I do that?

Answer 1

Sample data:
CREATE TABLE #Employee
(
ID integer NOT NULL,
EmployeeID integer NOT NULL,
[Status] varchar(8) NOT NULL,
EffectiveDate date NOT NULL,
CONSTRAINT [PK #Employee ID]
PRIMARY KEY CLUSTERED (ID)
);
INSERT #Employee
(ID, EmployeeID, [Status], EffectiveDate)
VALUES
(1, 110545, 'Active', '20110801'),
(2, 110700, 'Active', '20120105'),
(3, 110060, 'Active', '20120105'),
(4, 110222, 'Active', '20120630'),
(5, 110545, 'Resigned', '20120701'),
(6, 110545, 'Active', '20130212');
Helpful indexes:
CREATE NONCLUSTERED INDEX Active
ON #Employee
(EffectiveDate)
INCLUDE
(EmployeeID)
WHERE
[Status] = 'Active';
CREATE NONCLUSTERED INDEX Resigned
ON #Employee
(EmployeeID, EffectiveDate)
WHERE
[Status] = 'Resigned';
Solution with comments in-line:
CREATE TABLE #Selected (EmployeeID integer NOT NULL);
DECLARE
#start date = '20110101',
#end date = '20120801';
INSERT #Selected (EmployeeID)
SELECT
E.EmployeeID
FROM #Employee AS E
WHERE
-- Employees active before the end of the range
E.[Status] = 'Active'
AND E.EffectiveDate <= #end
AND NOT EXISTS
(
SELECT *
FROM #Employee AS E2
WHERE
-- No record of the employee
-- resigning before the start of the range
-- and after the active date
E2.EmployeeID = E.EmployeeID
AND E2.[Status] = 'Resigned'
AND E2.EffectiveDate >= E.EffectiveDate
AND E2.EffectiveDate <= #start
)
OPTION (RECOMPILE);
-- Return a distinct list of employees
SELECT DISTINCT
S.EmployeeID
FROM #Selected AS S;
Execution plan:
SQLFiddle here

Answer 2

1. Turn your events into ranges:
ID EmployeeID Status EffectiveDate ID EmployeeID Status StartDate EndDate
-- ---------- -------- ------------- -- ---------- -------- --------- ---------
1 110545 Active 01AUG2011 1 110545 Active 01AUG2011 01JUL2012
2 110700 Active 05JAN2012 2 110700 Active 05JAN2012 31DEC9999
3 110060 Active 05JAN2012 => 3 110060 Active 05JAN2012 31DEC9999
4 110222 Active 30JUN2012 4 110222 Active 30JUN2012 31DEC9999
5 110545 Resigned 01JUL2012 5 110545 Resigned 01JUL2012 12FEB2013
6 110545 Active 12FEB2013 6 110545 Active 12FEB2013 31DEC9999
2. Get active employees based on this condition:
WHERE Status = 'Active'
AND StartDate < #EndDate
AND EndDate > #StartDate
3. Count distinct EmployeeID values.
This is how you could implement the above:
WITH ranked AS (
SELECT
*,
rn = ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY EffectiveDate)
FROM EmployeeActivity
),
ranges AS (
SELECT
s.EmployeeID,
s.Status,
StartDate = s.EffectiveDate,
EndDate = ISNULL(e.EffectiveDate, '31DEC9999')
FROM ranked s
LEFT JOIN ranked e ON s.EmployeeID = e.EmployeeID AND s.rn = e.rn - 1
)
SELECT
ActiveCount = COUNT(DISTINCT EmployeeID)
FROM ranges
WHERE Status = 'Active'
AND StartDate < '01JAN2013'
AND EndDate > '01AUG2012'
;
A SQL Fiddle demo for this query: http://sqlfiddle.com/#!3/c3716/3

Answer 3

This should work (not tested)
SELECT COUNT DISTINCT EmployeeID FROM TABLE
WHERE EffectiveDate > CONVERT(VARCHAR(11), '08-01-2012', 106) AS [DDMONYYYY]
and EffectiveDate < CONVERT(VARCHAR(11), '01-01-2013', 106) AS [DDMONYYYY]
AND Status = 'Active'

Answer 4

Another solution using the PIVOT operator
DECLARE #StartDate date = '20120801',
#EndDate date = '20130101'
SELECT COUNT(*)
FROM (
SELECT EffectiveDate, EmployeeID, [Status]
FROM EmployeeActivity
WHERE EffectiveDate < #EndDate
) x
PIVOT
(
MAX(EffectiveDate) FOR [Status] IN([Resigned], [Active])
) p
WHERE ISNULL(Resigned, '99991231') > #StartDate
See demo on SQLFiddle

Answer 5

This should work fine:
DECLARE #d1 date = '01AUG2012';
DECLARE #d2 date = '01JAN2014';
WITH CTE_Before AS
(
--Last status of each employee before period will be RN=1
SELECT *, ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY EffectiveDate DESC) RN
FROM dbo.Table1
WHERE EffectiveDate < #d1
)
, CTE_During AS
(
--Those who become active during period
SELECT * FROM dbo.Table1
WHERE [Status] = 'Active' AND EffectiveDate BETWEEN #d1 AND #d2
)
--Union of those who were active at the beginning of period and those who became active during period
SELECT EmployeeID FROM CTE_Before WHERE RN = 1 AND Status = 'Active'
UNION
SELECT EmployeeID FROM CTE_During
SQLFiddle DEMO

Answer 6

You can use this query to build a list of employees and their start/resignation dates:
select
start.*,
resignation.EffectiveDate as ResignationDate
from Employment start
outer apply (
select top 1
Id,
EmployeeId,
EffectiveDate
from Employment
where EmployeeId = start.EmployeeId
and Status = 'Resigned'
and Id > start.Id
order by Id
) resignation
where start.Status='Active'
The key here is the use of OUTER APPLY, which allows us to use a pretty "funky" join criterion.
Here's how it works: http://www.sqlfiddle.com/#!3/ec969/7
From here, it's just a matter of querying the records whose the employment interval overlaps the target interval.
There are many ways to write this, but I personally like using a CTE, because I find it a bit more readable:
;with EmploymentPeriods as (
select
start.EmployeeId,
start.EffectiveDate as StartDate,
isnull(resignation.EffectiveDate, '9999-01-01') as EndDate
from Employment start
outer apply (
select top 1
Id,
EmployeeId,
EffectiveDate
from Employment
where EmployeeId = start.EmployeeId
and Status = 'Resigned'
and Id > start.Id
order by Id
) resignation
where start.Status='Active'
)
select distinct EmployeeId
from EmploymentPeriods
where EndDate >= #QueryStartDate
and StartDate <= #QueryEndDate
SQLFiddles:
first interval: http://www.sqlfiddle.com/#!3/ec969/27
second interval: http://www.sqlfiddle.com/#!3/ec969/26