MariaDB 10.2

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CREATE TABLE stocks
    (`time_fetched` datetime, `fetch_id` int, `name` varchar(6), `price` int)
;
    
INSERT INTO stocks
    (`time_fetched`, `fetch_id`, `name`, `price`)
VALUES
    ('2020-03-10 09:00:00', 1, 'stock1', 10),
    ('2020-03-10 09:00:00', 1, 'stock2', 15),
    ('2020-03-10 10:00:00', 2, 'stock1', 12),
    ('2020-03-10 10:00:00', 2, 'stock2', 20),
    ('2020-03-10 11:00:00', 3, 'stock1', 8),
    ('2020-03-10 11:00:00', 3, 'stock2', 18)
;
WITH prices AS (
  SELECT time_fetched, name, price,
         LAG(price, 1) OVER(PARTITION BY name ORDER BY time_fetched) AS price_1h,
         LAG(price, 2) OVER(PARTITION BY name ORDER BY time_fetched) AS price_2h
  FROM stocks
)
SELECT time_fetched, name, price,
       COALESCE(price - price_1h, 0) AS change_1h,
       COALESCE(price - price_2h, 0) AS change_2h
FROM prices


time_fetched
name
price
change_1h
change_2h


2020-03-10 09:00:00
stock1
10
0
0

2020-03-10 10:00:00
stock1
12
2
0

2020-03-10 11:00:00
stock1
8
-4
-2

2020-03-10 09:00:00
stock2
15
0
0

2020-03-10 10:00:00
stock2
20
5
0

2020-03-10 11:00:00
stock2
18
-2
3


WITH prices AS (
  SELECT time_fetched, name, price,
         LAG(price, 1) OVER(PARTITION BY name ORDER BY time_fetched) AS price_1h,
         LAG(price, 2) OVER(PARTITION BY name ORDER BY time_fetched) AS price_2h
  FROM stocks
)
SELECT time_fetched, name, price,
       price - price_1h AS change_1h,
       price - price_2h AS change_2h
FROM prices


time_fetched
name
price
change_1h
change_2h


2020-03-10 09:00:00
stock1
10
null
null

2020-03-10 10:00:00
stock1
12
2
null

2020-03-10 11:00:00
stock1
8
-4
-2

2020-03-10 09:00:00
stock2
15
null
null

2020-03-10 10:00:00
stock2
20
5
null

2020-03-10 11:00:00
stock2
18
-2
3

time_fetched	name	price	change_1h	change_2h
2020-03-10 09:00:00	stock1	10	0	0
2020-03-10 10:00:00	stock1	12	2	0
2020-03-10 11:00:00	stock1	8	-4	-2
2020-03-10 09:00:00	stock2	15	0	0
2020-03-10 10:00:00	stock2	20	5	0
2020-03-10 11:00:00	stock2	18	-2	3

time_fetched	name	price	change_1h	change_2h
2020-03-10 09:00:00	stock1	10	null	null
2020-03-10 10:00:00	stock1	12	2	null
2020-03-10 11:00:00	stock1	8	-4	-2
2020-03-10 09:00:00	stock2	15	null	null
2020-03-10 10:00:00	stock2	20	5	null
2020-03-10 11:00:00	stock2	18	-2	3