How to build in product expiration in SQL? - sql

Question

I have a table that looks like the following and from it I want to get days remaining of total doses:
USER|PURCHASE_DATE|DOSES
1111|2017-07-27|15
2222|2020-07-17|3
3333|2021-02-01|5
If the doses do not have an expiration and each can be used for 90 days then the SQL I use is:
SUM(DOSES)*90-DATEDIFF(DAY,MIN(DATE),GETDATE())
USER|DAYS_REMAINING
1111|0
2222|6
3333|385
But what if I want to impose an expiration of each dose at a year? What can I do to modify my SQL to get the following desired answer:
USER|DAYS_REMAINING
1111|-985
2222|6
3333|300
It probably involves taking the MIN between when doses expire and how long they would last but I don't know how to aggregate in the expiry logic.

Answer 1

MIN is a aggregate function you want LEAST to pick between the two values:
WITH data(user,purchase_date, doses) AS (
SELECT * FROM VALUES
(1111,'2017-07-27',15),
(2222,'2020-07-17',3),
(3333,'2021-02-01',5)
)
SELECT
d.*,
d.doses * 90 AS doses_duration,
365::number AS year_duration,
least(doses_duration, year_duration) as max_duration,
DATEADD('day', max_duration, d.purchase_date)::date as last_dose_day,
DATEDIFF('day', current_date, last_dose_day) as day_remaining
FROM data AS d
ORDER BY 1;
gives:
USER PURCHASE_DATE DOSES DOSES_DURATION YEAR_DURATION MAX_DURATION LAST_DOSE_DAY DAY_REMAINING
1111 2017-07-27 15 1350 365 365 2018-07-27 -986
2222 2020-07-17 3 270 365 270 2021-04-13 5
3333 2021-02-01 5 450 365 365 2022-02-01 299
which can all be rolled together with a tiny fix on the date_diff, as:
WITH data(user,purchase_date, doses) AS (
SELECT * FROM VALUES
(1111,'2017-07-27',15),
(2222,'2020-07-17',3),
(3333,'2021-02-01',5)
)
SELECT
d.user,
DATEDIFF('day', current_date, DATEADD('day', least(d.doses * 90, 365::number), d.purchase_date)::date)+1 as day_remaining
FROM data AS d
ORDER BY 1;
giving:
USER DAY_REMAINING
1111 -985
2222 6
3333 300