create date range report based on history table - sql-server

Question

We have been keeping track of some changes in a History Table like this:
ChangeID EmployeeID PropertyName OldValue NewValue ModifiedDate
100 10 EmploymentStart Not Set 1 2013-01-01
101 10 SalaryValue Not Set 55000 2013-01-01
102 10 SalaryValue 55000 61500 2013-03-20
103 10 SalaryEffectiveDate 2013-01-01 2013-04-01 2013-03-20
104 11 EmploymentStart Not Set 1 2013-01-21
105 11 SalaryValue Not Set 43000 2013-01-21
106 10 SalaryValue 61500 72500 2013-09-20
107 10 SalaryEffectiveDate 2013-04-01 2013-10-01 2013-09-20
Basically if an Employee's Salary changes, we log two rows in the history table. One row for the Salary value itself and the other row for the salary effective date. So these two have identical Modification Date/Time and are kind safe to assume that are always after each other in the database. We can also assume that Salary Value is always logged first (so it is one record before the corresponding effective date
Now we are looking into creating reports based on a given date range into a table like this:
Annual Salary Change Report (2013)
EmployeeID Date1 Date2 Salary
10 2013-01-01 2013-04-01 55000
10 2013-04-01 2013-10-01 61500
10 2013-10-01 2013-12-31 72500
11 2013-03-21 2013-12-31 43000
I have done something similar in the past by joining the table to itself but in those cases the effective date and the new value where in the same row. Now I have to create each row of the output table by looking into a few rows of the existing history table. Is there an straightforward way of doing this whitout using cursors?
Edit #1:
Im reading on this and apparently its doable using PIVOTs
Thank you very much in advance.

Answer 1

You can use self join to get the result you want. The trick is to create a cte and add two rows for each EmployeeID as follows (I call the history table ht):
with cte1 as
(
select EmployeeID, PropertyName, OldValue, NewValue, ModifiedDate
from ht
union all
select t1.EmployeeID,
(case when t1.PropertyName = "EmploymentStart" then "SalaryEffectiveDate" else t1.PropertyName end),
(case when t1.PropertyName = "EmploymentStart" then t1.ModifiedDate else t1.NewValue end),
(case when t1.PropertyName = "SalaryValue" then t1.NewValue
when t1.PropertyName = "SalaryEffectiveDate" then "2013-12-31"
when t1.PropertyName = "EmploymentStart" then "2013-12-31" end),
"2013-12-31"
from ht t1
where t1.ModifiedDate = (select max(t2.ModifiedDate) from ht t2 where t1.EmployeeID = t2.EmployeeID)
)
select t3.EmployeeID, t4.OldValue Date1, t4.NewValue Date2, t3.OldValue Salary
from cte1 t3
inner join cte1 t4 on t3.EmployeeID = t4.EmployeeID
and t3.ModifiedDate = t4.ModifiedDate
where t3.PropertyName = "SalaryValue"
and t4.PropertyName = "SalaryEffectiveDate"
order by t3.EmployeeID, Date1
I hope this helps.

Answer 2

It is a little over kill to use pivot since you only need two properties. Use GROUP BY can also achieve this:
;WITH cte_salary_history(EmployeeID,SalaryEffectiveDate,SalaryValue)
AS
(
SELECT EmployeeID,
MAX(CASE WHEN PropertyName='SalaryEffectiveDate' THEN NewValue ELSE NULL END) AS SalaryEffectiveDate,
MAX(CASE WHEN PropertyName='SalaryValue' THEN NewValue ELSE NULL END) AS SalaryValue
FROM yourtable
GROUP BY EmployeeID,ModifiedDate
)
SELECT EmployeeID,SalaryEffectiveDate,
LEAD(SalaryEffectiveDate,1,'9999-12-31') OVER(PARTITION BY EmployeeID ORDER BY SalaryEffectiveDate) AS SalaryEndDate,
SalaryValue
FROM cte_salary_history