Question

I have a table, employee history with the following

ID | Current_Dept | Dept_Start_Date | Name
1 | Sales | 2012-01-01 | John Smith
1 | Marketing | 2010-01-01 | John Smith
1 | Intern | 2008-01-01 | John Smith
2 | IT | 2012-01-01 | Sue Jones
2 | Sales | 2011-01-01 | Sue Jones
2 | eBusiness | 2010-10-01 | Sue Jones
3 | Warehouse | 2012-01-01 | Bobby Ray
3 | Sales | 2009-01-01 | Bobby Ray

What I would like is a query giving everyone who ever worked in Sales:

ID | DeptBefore | DeptAfter | CurrentDept
1  | Marketing  |           | Sales
2  | ebusiness  | IT        | IT
3  |            | Warehouse | Warehouse

At the moment I see no simpler way of doing this other then recursively querying the table for each row.

I’m tempted to create a ‘temp’ table that’s populated once a day and run the query off of that.

I’m using SQL Server and C# (ASP.NET) incase these offer other simpler solutions.

I hope that all makes sense.

Thanks,

Answer 1

From your data it appears that you want the departments immediately before and after the sales department. For example; you don’t show that John Smith started as an intern.

NOTE: You may want to consider the results you want if someone has worked for sales on two different occasions.

WITH
  sequenced AS
(
  SELECT
    *,
    ROW_NUMBER() OVER (PARTITION BY id ORDER BY dept_start_date DESC) AS sequence_id
  FROM
    yourTable
)
SELECT
  salesRecord.id,
  prevRecord.current_dept     AS DeptBefore,
  nextRecord.current_dept     AS DeptAfter,
  lastRecord.current_dept     AS DeptCurrent
FROM
  sequenced     AS salesRecord
LEFT JOIN
  sequenced     AS prevRecord
    ON  prevRecord.id          = salesRecord.id
    AND prevRecord.sequence_id = salesRecord.sequence_id - 1
LEFT JOIN
  sequenced     AS nextRecord
    ON  nextRecord.id          = salesRecord.id
    AND nextRecord.sequence_id = salesRecord.sequence_id + 1
LEFT JOIN
  sequenced     AS lastRecord
    ON  lastRecord.id          = salesRecord.id
    AND lastRecord.sequence_id = 1
WHERE
  salesRecord.CurrentDept = 'Sales'

By ordering the items in Descending order, the current record is always sequence_id = 1.