select
year 1,count(*),
year 2, count(*)
From db
WHERE year1 >= DATEADD(yy,-1,DATEADD(yy,DATEDIFF(yy,0,GETDATE()),0))
AND year1 <= DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()) - 12, 0)
AND
year2 >= DATEADD(yy,0,DATEADD(yy,DATEDIFF(yy,0,GETDATE()),0))
AND year2 <= DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()) , 0)

2016 Units  2017 units
   3000        1200