Select latest available SQL entry state - sql

Question

Consider this DDL:
CREATE TABLE cash_depot_state
(
id INTEGER NOT NULL PRIMARY KEY,
date DATE,
amount REAL,
cash_depot_id INTEGER
);
INSERT INTO cash_depot_state (date, amount, cash_depot_id)
VALUES (DATE('2022-03-02'), 382489, 5);
INSERT INTO cash_depot_state (date, amount, cash_depot_id)
VALUES (DATE('2022-03-03'), 750, 2);
INSERT INTO cash_depot_state (date, amount, cash_depot_id)
VALUES (DATE('2022-03-04'), 750, 3);
INSERT INTO cash_depot_state (date, amount, cash_depot_id)
VALUES (DATE('2022-03-05'), 0, 5);
For an array of dates I need to select sum of all cash depots' actual amounts:
2022-03-01 - no data available - expect 0
2022-03-02 - cash depot #5 has changed it's value to 382489 - expect 382489
2022-03-03 - cash depot #2 has changed it's value to 750 - expect 382489 + 750
2022-03-03 - cash depot #3 has changed it's value to 750 - expect 382489 + 750 + 750
2022-03-04 - cash depot #5 has changed it's value to 0 - expect 0 + 750 + 750
My best attempt: http://sqlfiddle.com/#!5/94ad0d/1
But I can't figure out how to pick winner of a subgroup

Answer 1

You could define the latest amount per cash depot as the record that has row number 1, when you divvy up records by cash_depot_id, and order them descending by date:
SELECT
id,
cash_depot_id,
date,
amount,
ROW_NUMBER() OVER (PARTITION BY cash_depot_id ORDER BY date DESC) rn
FROM
cash_depot_state
This will highlight the latest data from your table - all the relevant rows will have rn = 1:
id
cash_depot_id
date
amount
rn
2
2
2022-03-03
750.0
1
3
3
2022-03-04
750.0
1
4
5
2022-03-05
0.0
1
1
5
2022-03-02
382489.0
2
Now you can use a WHERE clause to filter records to a certain date, e.g. WHERE data <= '2022-03-05':
SELECT
SUM(amount) sum_amount
FROM
(
SELECT amount, ROW_NUMBER() OVER (PARTITION BY cash_depot_id ORDER BY date DESC) rn
FROM cash_depot_state
WHERE date <= '2022-03-05'
) latest
WHERE
rn = 1;
will return 1500.
A more traditional way to solve this would be a correlated sub-query:
SELECT
SUM(amount) sum_amount
FROM
cash_depot_state s
WHERE
date = (
SELECT MAX(date)
FROM cash_depot_state
WHERE date <= '2022-03-05' AND cash_depot_id = s.cash_depot_id
)
or a join against a materialized sub-query:
SELECT
SUM(amount) sum_amount
FROM
cash_depot_state s
INNER JOIN (
SELECT MAX(date) date, cash_depot_id
FROM cash_depot_state
WHERE date <= '2022-03-05'
GROUP BY cash_depot_id
) latest ON latest.cash_depot_id = s.cash_depot_id AND latest.date = s.date
In large tables, these are potentially faster than the ROW_NUMBER() variant. YMMV, take measurements.
An index that covers date, cash_depot_id, and amount helps all shown approaches:
CREATE INDEX ix_latest_cash ON cash_depot_state (date DESC, cash_depot_id ASC, amount);
To run against a CTE that produces a calendar, any of the above can be correlated as a subquery
WITH RECURSIVE dates(date) AS (
SELECT '2022-03-01'
UNION ALL
SELECT date(date, '+1 day') FROM dates WHERE date < DATE('now')
)
SELECT
date,
IFNULL(
(
-- any of the above approaches with `WHERE date <= dates.date`
), 0
) balance
FROM
dates;
e.g. http://sqlfiddle.com/#!5/94ad0d/12