DataSet - How to retrieve values from grouped columns?

I have SQL which return data:

SELECT
dbo.TOWARY.TWR_NUMER AS INDEKS,
dbo.TOWARY.TWR_NAZWA AS NAZWA,
dbo.SL_JM.SLJM_KOD AS JM,
SUM (dbo.WAZENIA.WZN_ILOSC * dbo.WZN_CNY.WZNCNY_NETTO) / SUM (dbo.WAZENIA.WZN_ILOSC) AS CENA,
DATEPART(yyyy, dbo.ZAKUPY.ZKP_DATA_ZAKUPU) AS ROK,
dbo.MAGAZYNY.MG_KOD AS MG_KOD,
dbo.MAGAZYNY.MG_NAZWA AS MG_NAZWA,

ROW_NUMBER () OVER (
        PARTITION BY
        dbo.TOWARY.TWR_NUMER
       ORDER BY
       dbo.TOWARY.TWR_NUMER,
       DATEPART(yyyy, dbo.ZAKUPY.ZKP_DATA_ZAKUPU) DESC
) AS NUMER

[ROK] - Year the number of columns is variable

I grouped the columns by: year.

I want to divide the years between them, e.g.: 2021/2020 2022/2021 2023/2022 (...)

for rows (Example 20001):

0,61 / 0,64

0,74 / 0,64

But i don't know how take value from Column (Year)?

%First / Last

=(First(Fields!CENA.Value, "INDEKS")-Last(Fields!CENA.Value, "INDEKS"))/Last(Fields!CENA.Value, "INDEKS")