How to generate rows from date to date with the same data? - postgresql

Question

In my database I have a row like this:
id type date price
1 A 2022-11-09 100
2 A 2022-11-12 200
Provided I want to have a price for type A from day 9 to day 15 of November, my expectation result for this query is like this
type date price
A 2022-11-09 100
A 2022-11-10 100
A 2022-11-11 100
A 2022-11-12 200
A 2022-11-13 200
A 2022-11-14 200
A 2022-11-15 200
I wonder if is there anyway we can do it by query

Answer 1

Since you want your output to have a row per date in that range, let's start from generate_series to put that range together:
SELECT series.date::date
FROM generate_series('2022-11-09', '2022-11-15', INTERVAL '1 day') series;
date
------------
2022-11-09
2022-11-10
2022-11-11
2022-11-12
2022-11-13
2022-11-14
2022-11-15
(7 rows)
Then we can fill in the price column using a subquery:
SELECT
'A' as type,
series.date::date,
(
SELECT price
FROM mytable
WHERE type = 'A'
AND date <= series.date
ORDER BY date DESC
LIMIT 1
) as price
FROM generate_series('2022-11-09', '2022-11-15', interval '1 day') series;
type | date | price
------+------------+-------
A | 2022-11-09 | 100
A | 2022-11-10 | 100
A | 2022-11-11 | 100
A | 2022-11-12 | 200
A | 2022-11-13 | 200
A | 2022-11-14 | 200
A | 2022-11-15 | 200
(7 rows)
Another approach might be to create ranges out of the data using a LEAD window function:
SELECT
type,
daterange(date, LEAD(date) OVER (PARTITION BY type ORDER BY date)) as range,
price
FROM mytable;
type | range | price
------+-------------------------+-------
A | [2022-11-09,2022-11-12) | 100
A | [2022-11-12,) | 200
(2 rows)
And then join our generate_series with the ranges using the inclusion operator:
WITH ranges AS (
SELECT
type,
daterange(date, LEAD(date) OVER (PARTITION BY type ORDER BY date)) as range,
price
FROM mytable
)
SELECT type, series.date::date, price
FROM generate_series('2022-11-09', '2022-11-15', interval '1 day') series
JOIN ranges ON (ranges.range #> series.date)
WHERE type = 'A';
type | date | price
------+------------+-------
A | 2022-11-09 | 100
A | 2022-11-10 | 100
A | 2022-11-11 | 100
A | 2022-11-12 | 200
A | 2022-11-13 | 200
A | 2022-11-14 | 200
A | 2022-11-15 | 200
(7 rows)