Return row of every n'th record

Question

How can I return every nth record from a sub query based on a numerical parameter that I supply?

For example, I may have the following query:

Answer 1

Select B.name 
from (Select row_number() over (order by ordering) as row_num, 
      A.name 
      from (Select name,'P1' as ordering 
            from [dbo].[every_2nd_record]
           ) A
      ) B
where B.row_num%2=0

Answer 2

This is where ROW_NUMBER can help. It requires an order-by clause but this is okay because an order-by is present (and required to guarantee a particular order).

SELECT t.id, t.key
FROM
(
    SELECT id, key, ROW_NUMBER() OVER (ORDER BY key) AS rownum
    FROM datatable
) AS t
WHERE t.rownum % 30 = 0    -- or % 40 etc
ORDER BY t.key

Answer 3

You don't have to use row number, any integer field will do. On most tables we have an autonumber field. For simplicity, I will call it ID. To display every 13th record:

Select ID, LastName, FirstName FROM Users WHERE ID%13 = 0 ORDER BY ID