Oracle 21c

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create table sales (year_1 number, total_sale number);
insert into sales values (2015,23000);
1 rows affected

insert into sales values (2016,25000);
1 rows affected

insert into sales values (2017,34000);
1 rows affected

insert into sales values (2018,32000);
1 rows affected

insert into sales values (2019,33000);
1 rows affected

select year_1, total_sale as current_total_sale, 
lag(total_sale) over (order by null) as previous_total_sale,
total_sale - lag(total_sale) over (order by null) difference
from sales;


YEAR_1
CURRENT_TOTAL_SALE
PREVIOUS_TOTAL_SALE
DIFFERENCE


2015
23000
null
null

2016
25000
23000
2000

2017
34000
25000
9000

2018
32000
34000
-2000

2019
33000
32000
1000

YEAR_1	CURRENT_TOTAL_SALE	PREVIOUS_TOTAL_SALE	DIFFERENCE
2015	23000	null	null
2016	25000	23000	2000
2017	34000	25000	9000
2018	32000	34000	-2000
2019	33000	32000	1000