SQL Server : how to select a fixed amount of rows (select every x-th value)

Question

A short description: I have a table with data that is updated over a certain time period. Now the problem is, that - depending on the nature of the sensor which sends the da

Answer 1

In essence, all you need to do to select the x-th value is retain all rows where the modulus of the rownumber divided by x is 0.

WHERE rn % @x_thValues = 0

Now to be able to use your ROW_NUMBER's result, you'll need to wrap the entire statement into in a subselect

SELECT  *
FROM    (
            SELECT  *
                    , rn = ROW_NUMBER() OVER (ORDER BY Value)
            FROM    DummyData
        ) d
WHERE   rn % @x_thValues = 0                    

Combined with a variable to what x-th values you need, you might use something like this testscript

DECLARE @x_thValues INTEGER = 2

;WITH DummyData AS (SELECT * FROM (VALUES (1), (2), (3), (4)) v (Value))
SELECT  *
FROM    (
            SELECT  *
                    , rn = ROW_NUMBER() OVER (ORDER BY Value)
            FROM    DummyData
        ) d
WHERE   rn % @x_thValues = 0