SQL Find pairs of data in rows and convert to columns - sql-server

Question

I'm trying to setup a query to pull employee tenure reports. I have an employee status table that tracks information for each employee (e.g. -Hire Date, Term Date, Salary Change, etc.) The table looks like this:
EmployeeID | Date | Event
1 | 1/1/99 | 1
2 | 1/2/99 | 1
1 | 1/3/99 | 2
1 | 1/4/99 | 1
I used a pivot table to move the table from a vertical layout to a horizontal layout
SELECT [FK_EmployeeID], MAX([1]) AS [Hire Date], ISNULL(MAX([2]), DATEADD(d, 1, GETDATE())) AS [Term Date]
FROM DT_EmployeeStatusEvents PIVOT (MAX([Date]) FOR [EventType] IN ([1], [2])) T
GROUP BY [FK_EmployeeID]
I get a result like this:
EmployeeID | 1 | 2
1 | 1/4/99 | 1/3/99
2 | 1/2/99 | *null*
However, the problem I run into is that I need both sets of values for each employee. (We hire a lot of recurring seasonals) What I would like is a way to convert the columns to rows selecting the hire date (1) and the very next term date (2) for each employee like this:
EmployeeID | 1 | 2
1 | 1/1/99 | 1/3/99
2 | 1/2/99 | *null*
1 | 1/4/99 | *null*
Is this possible? I've looked at a lot of the PIVOT examples and they all show an aggregate function.

Answer 1

The problem is that you are attempting to pivot a datetime value so you are limited to using either max or min as the aggregate function. When you use those you will only return one row for each employeeid.
In order to get past this you will need to have some value that will be used during the grouping of your data - I would suggest using a windowing function like row_number(). You can make your subquery:
select employeeid, date, event
, row_number() over(partition by employeeid, event
order by date) seq
from DT_EmployeeStatusEvents
See SQL Fiddle with Demo. This creates a unique value for each employeeId and event combination. This new number will then be grouped on so you can return multiple rows. You full query will be:
select employeeid, [1], [2]
from
(
select employeeid, date, event
, row_number() over(partition by employeeid, event
order by date) seq
from DT_EmployeeStatusEvents
) d
pivot
(
max(date)
for event in ([1], [2])
) piv
order by employeeid;
See SQL Fiddle with Demo

Answer 2

This should get you started...
DECLARE #EMP TABLE (EMPID INT, dDATE DATETIME, EVENTTYPE INT)
INSERT INTO #EMP
SELECT 1,'1/1/99',1 UNION ALL
SELECT 2,'1/2/99',1 UNION ALL
SELECT 1,'1/3/99',2 UNION ALL
SELECT 1,'1/4/99',1
SELECT EMPID, HIRE, TERM
FROM (SELECT EMPID, dDATE, 'HIRE' AS X, ROW_NUMBER() OVER(PARTITION BY EMPID, EVENTTYPE ORDER BY DDATE) AS INSTANCE FROM #EMP WHERE EVENTTYPE=1
UNION ALL
SELECT EMPID, dDATE, 'TERM' AS X, ROW_NUMBER() OVER(PARTITION BY EMPID, EVENTTYPE ORDER BY DDATE) AS INSTANCE FROM #EMP WHERE EVENTTYPE=2) DATATABLE
PIVOT (MIN([DDATE])
FOR X IN ([HIRE],[TERM])) PIVOTTABLE