В SQL Server можете да го направите по следния начин:
;WITH CTE AS(
SELECT ROW_NUMBER() OVER(PARTITION BY CAST(wavelength AS INT)-CAST(wavelength AS INT)%10 ORDER BY wavelength) AS ROW_ID,wavelength,reflectance FROM Your_Table
)
SELECT wavelength,reflectance FROM CTE WHERE ROW_ID=1
Надявам се, че ще помогне.
