Question

Suppose I have this data:

Employee  Task   IsCurrent
--------  ----   ---------
Jeff      1      Yes
Jeff      2      No
Jane      1      No
Jane      2      Yes
Jane      3      No
Jane      4      No
Jake      1      Yes

Employees have some number of tasks, and one of them will be current. The task number indicates an ordering — they perform tasks in order, looping back to the beginning when they’re done with the last one. I’d like a query to see the next three tasks. I’d like this result set:

Employee    CurrentTask  NextTask  NextTask2
--------    -----------  --------  ---------
Jeff        1            2         1
Jane        2            3         4
Jake        1            1         1

Is this possible? I’m using SQL 2005

UPDATE: Sorry, I didn’t make clear that the task numbers aren’t necessarily sequental — i.e. Mike might actually have tasks 10, 23, and 223. So I can’t just join looking for the next sequential task number.

Answer 1

Use:

WITH summary AS (
   SELECT t.employee,
          t.task,
          t.iscurrent,
          ROW_NUMBER() OVER (PARTITION BY t.employee
                                 ORDER BY t.task) AS rank
     FROM TABLE t)
   SELECT a.employee,
          a.task AS current_task,
          COALESCE(b.task, y.min_task) AS next_task,
          COALESCE(c.task, y.min_task) AS next_task2
     FROM summary a
     JOIN (SELECT x.employee,
                  MIN(x.task) AS min_task
             FROM TABLE x
         GROUP BY x.employee) y ON y.employee = a.employee
LEFT JOIN summary b ON b.employee = a.employee
                   AND b.rank = a.rank + 1
LEFT JOIN summary c ON c.employee = a.employee
                   AND c.rank = a.rank + 2                   
    WHERE a.iscurrent = 'yes'

Like I said earlier, would be easier if SQL Server supported LEAD/LAG functions…