Calculate the period of validity of the price - mysql

Question

I have a table with an item, its cost and the date it was added.
CREATE TABLE item_prices (
item_id INT,
item_name VARCHAR(30),
item_price DECIMAL(12, 2),
created_dttm DATETIME
);
INSERT INTO item_prices(item_id, item_name, item_price, created_dttm) VALUES
(1, 'spoon', 10.20 , '2023-01-01 01:00:00'),
(1, 'spoon', 10.20 , '2023-01-08 01:35:00'),
(1, 'spoon', 10.35 , '2023-01-14 15:00:00'),
(2, 'table', 40.00 , '2023-01-01 01:00:00'),
(2, 'table', 40.00 , '2023-01-03 11:22:00'),
(2, 'table', 41.00 , '2023-01-10 08:28:22'),
(1, 'spoon', 10.35 , '2023-01-28 21:52:00'),
(1, 'spoon', 11.00 , '2023-02-15 16:36:00'),
(2, 'table', 41.00 , '2023-02-16 21:42:11'),
(2, 'table', 45.20 , '2023-02-19 20:25:25'),
(1, 'spoon', 9.00 , '2023-03-02 14:50:00'),
(1, 'spoon', 9.00 , '2023-03-06 16:36:00'),
(1, 'spoon', 8.50 , '2023-03-15 12:00:00'),
(2, 'table', 30 , '2023-03-05 10:10:10'),
(2, 'table', 30 , '2023-03-10 15:45:00');
I need to create a new table with the following fields:
"item_id",
"item_name",
"item_price",
"valid_from_dt": date on which the price was effective (created_dttm price record)
"valid_to_dt": date until which this price was valid (created_dttm of the next record for this product "minus" one day)
I thought it might be possible to start by selecting days on which new entries are added with new prices with such a request:
SELECT item_id, item_name, item_price,
MIN(created_dttm) as dt
FROM table
GROUP BY item_price, item_id, item_name
that provides me this output:
The expected output is the following:
item_id
item_name
item_price
valid_from_dt
valid_to_dt
1
spoon
10.20
2023-01-01
2023-01-13
1
spoon
10.35
2023-01-14
2023-02-14
1
spoon
11.00
2023-02-15
2023-03-01
1
spoon
9.00
2023-03-02
2023-03-01
1
spoon
8.50
2023-03-15
2023-03-14
2
table
40.00
2023-01-01
2022-01-09
2
table
41.00
2023-01-10
2023-02-18
....
....
....
....
....

Answer 1

select distinct
item_id,
item_name,
first_value(item_price) over (partition by item_id order by created_dttm) as item_price,
min(created_dttm) over (partition by item_id ) as valid_from_dt,
max(created_dttm) over (partition by item_id ) as valid_to_dt
from item_prices
;
output:
item_id
item_name
item_price
valid_from_dt
valid_to_dt
1
spoon
10.20
2023-01-01 01:00:00
2023-03-15 12:00:00
2
table
40.00
2023-01-01 01:00:00
2023-03-10 15:45:00
see: DBFIDDLE

Answer 2

Your query is correct. It's only missing the next step:
retrieving the next "valid_from_dt" in the partition <item_id, item_name>, using the LEAD function
subtract 1 day from it
WITH cte AS (
SELECT item_id, item_name, item_price,
MIN(created_dttm) AS valid_from_dt
FROM item_prices
GROUP BY item_id, item_name, item_price
)
SELECT *,
LEAD(valid_from_dt) OVER(PARTITION BY item_id, item_name) - INTERVAL 1 DAY AS valid_to_dt
FROM cte
Check the demo here.