SQL Server 2017

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create table yourTable (year int, month int, product int, units int);
insert into yourTable (year, month, product, units)
values (2017,1,1,1721);
insert into yourTable (year, month, product, units)
values (2017,2,1,4915);
insert into yourTable (year, month, product, units)
values (2017,4,2,2933);
insert into yourTable (year, month, product, units)
values (2017,5,1,5230);
insert into yourTable (year, month, product, units)
values (2018,1,2,7672);
insert into yourTable (year, month, product, units)
values (2018,2,1,5216);
insert into yourTable (year, month, product, units)
values (2018,3,1,8911);
7 rows affected

select distinct
  coalesce(a.year, b.year+1) as year
  , coalesce(a.month, b.month) as month
  , coalesce(a.product, b.product) as product
  , a.units as units
  , b.units as units_prev
from yourtable a
full join yourtable b on a.[year] = b.[year]+1 and a.[month] = b.[month] and a.product = b.product




year
month
product
units
units_prev


2017
1
1
1721
null

2017
2
1
4915
null

2017
4
2
2933
null

2017
5
1
5230
null

2018
1
1
null
1721

2018
1
2
7672
null

2018
2
1
5216
4915

2018
3
1
8911
null

2018
4
2
null
2933

2018
5
1
null
5230

2019
1
2
null
7672

2019
2
1
null
5216

2019
3
1
null
8911

year	month	product	units	units_prev
2017	1	1	1721	null
2017	2	1	4915	null
2017	4	2	2933	null
2017	5	1	5230	null
2018	1	1	null	1721
2018	1	2	7672	null
2018	2	1	5216	4915
2018	3	1	8911	null
2018	4	2	null	2933
2018	5	1	null	5230
2019	1	2	null	7672
2019	2	1	null	5216
2019	3	1	null	8911