I'm using SQL Server 2008 R2. I have table called EmployeeHistory with the following structure and sample data:
EmployeeID Date DepartmentID SupervisorID 10001 20130101 001 10009 10001 20130909 001 10019 10001 20131201 002 10018 10001 20140501 002 10017 10001 20141001 001 10015 10001 20141201 001 10014
Notice that the Employee 10001 has been changing 2 departments and several supervisors over time. What I am trying to do is to list the start and end dates of this employee's employment in each Department ordered by the Date field. So, the output will look like this:
EmployeeID DateStart DateEnd DepartmentID 10001 20130101 20131201 001 10001 20131201 20141001 002 10001 20141001 NULL 001
I intended to use partitioning the data using the following query but it failed. The Department changes from 001 to 002 and then back to 001. Obviously I cannot partition by DepartmentID... I'm sure I'm overlooking the obvious. Any help? Thank you, in advance.
SELECT * ,ROW_NUMBER() OVER (PARTITION BY EmployeeID, DepartmentID ORDER BY [Date]) RN FROM EmployeeHistory
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~ Asked on 2013-11-12 05:10:29
A bit involved. Easiest would be to refer to this SQL Fiddle I created for you that produces the exact result. There are ways you can improve it for performance or other considerations, but this should hopefully at least be clearer than some alternatives.
The gist is, you get a canonical ranking of your data first, then use that to segment the data into groups, then find an end date for each group, then eliminate any intermediate rows. ROW_NUMBER() and CROSS APPLY help a lot in doing it readably.
The SQL Fiddle does in fact seem to be broken, for some reason, but it appears to be a problem on the SQL Fiddle site. Here's a complete version, tested just now on SQL Server 2016:
CREATE TABLE Source ( EmployeeID int, DateStarted date, DepartmentID int ) INSERT INTO Source VALUES (10001,'2013-01-01',001), (10001,'2013-09-09',001), (10001,'2013-12-01',002), (10001,'2014-05-01',002), (10001,'2014-10-01',001), (10001,'2014-12-01',001) SELECT *, ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY DateStarted) AS EntryRank, newid() as GroupKey, CAST(NULL AS date) AS EndDate INTO #RankedData FROM Source ; UPDATE #RankedData SET GroupKey = beginDate.GroupKey FROM #RankedData sup CROSS APPLY ( SELECT TOP 1 GroupKey FROM #RankedData sub WHERE sub.EmployeeID = sup.EmployeeID AND sub.DepartmentID = sup.DepartmentID AND NOT EXISTS ( SELECT * FROM #RankedData bot WHERE bot.EmployeeID = sup.EmployeeID AND bot.EntryRank BETWEEN sub.EntryRank AND sup.EntryRank AND bot.DepartmentID <> sup.DepartmentID ) ORDER BY DateStarted ASC ) beginDate (GroupKey); UPDATE #RankedData SET EndDate = nextGroup.DateStarted FROM #RankedData sup CROSS APPLY ( SELECT TOP 1 DateStarted FROM #RankedData sub WHERE sub.EmployeeID = sup.EmployeeID AND sub.DepartmentID <> sup.DepartmentID AND sub.EntryRank > sup.EntryRank ORDER BY EntryRank ASC ) nextGroup (DateStarted); SELECT * FROM ( SELECT *, ROW_NUMBER() OVER (PARTITION BY GroupKey ORDER BY EntryRank ASC) AS GroupRank FROM #RankedData ) FinalRanking WHERE GroupRank = 1 ORDER BY EntryRank; DROP TABLE #RankedData DROP TABLE Source
~ Answered on 2013-11-12 05:53:13
I would do something like this:
;WITH x AS (SELECT *, Row_number() OVER( partition BY employeeid ORDER BY datestart) rn FROM employeehistory) SELECT * FROM x x1 LEFT OUTER JOIN x x2 ON x1.rn = x2.rn + 1
Or maybe it would be x2.rn - 1. You'll have to see. In any case, you get the idea. Once you have the table joined on itself, you can filter, group, sort, etc. to get what you need.
~ Answered on 2013-11-12 05:19:55