How to find the next value within a table based on certain criteria

Question

I have a table:

ID | Name | Date
 1 | ABC  | 2015-01-01
 2 | XYZ  | 2015-01-02
 3 | ABC  | 2015-01-03
 4 | ABC  | 2015-01-04

I want to query this table such a way that the result becomes:

ID | Name | Date       | NextDate
 1 | ABC  | 2015-01-01 | 2015-01-03
 2 | XYZ  | 2015-01-02 | null
 3 | ABC  | 2015-01-03 | 2015-01-04
 4 | ABC  | 2015-01-04 | null

One Solution is:

select t1.*,
  (select min(t2.Date) from TAB t2 where t2.ID > t1.ID t2.Name = t1.Name) NextDate
from TAB t1

But this is very slow as we are doing aggregation on each row. Is there any alternative solution to this which is more efficient than above ?

Answer 1

Since SQL SERVER 2008 does not support LEAD window function we have to simulate it using row_number and self join. Try this

;WITH cte
     AS (SELECT t1.*,
                Row_number()
                  OVER(
                    partition BY Name
                    ORDER BY [Date]) AS rn
         FROM   TAB t1)
SELECT a.ID,a.Name,a.Date,b.Date as nextdate
FROM   cte a
       LEFT OUTER JOIN cte b
                    ON a.Name = b.Name
                       AND a.rn + 1 = b.rn ORDER BY a.ID