Query with dynamic date intervals - mysql

Question

Given a statuses table that holds information about products availability, how do I select the date that corresponds to the 1st day in the latest 20 days that the product has been active?
Yes I know the question is hard to follow. I think another way to put it would be: I want to know how many times each product has been sold in the last 20 days that it was active, meaning the product could have been active for years, but I'd only want the sales count from the latest 20 days that it had a status of "active".
It's something easily doable in the server-side (i.e. getting any collection of products from the DB, iterating them, performing n+1 queries on the statuses table, etc), but I have hundreds of thousands of items so it's imperative to do it in SQL for performance reasons.
table : products
+-------+-----------+
| id | name |
+-------+-----------+
| 1 | Apple |
| 2 | Banana |
| 3 | Grape |
+-------+-----------+
table : statuses
+-------+-------------+---------------+---------------+
| id | name | product_id | created_at |
+-------+-------------+---------------+---------------+
| 1 | active | 1 | 2018-01-01 |
| 2 | inactive | 1 | 2018-02-01 |
| 3 | active | 1 | 2018-03-01 |
| 4 | inactive | 1 | 2018-03-15 |
| 6 | active | 1 | 2018-04-25 |
| 7 | active | 2 | 2018-03-01 |
| 8 | active | 3 | 2018-03-10 |
| 9 | inactive | 3 | 2018-03-15 |
+-------+-------------+---------------+---------------+
table : items (ordered products)
+-------+---------------+-------------+
| id | product_id | order_id |
+-------+---------------+-------------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 3 | 1 | 3 |
| 4 | 1 | 4 |
| 5 | 1 | 5 |
| 6 | 2 | 3 |
| 7 | 2 | 4 |
| 8 | 2 | 5 |
| 9 | 3 | 5 |
+-------+---------------+-------------+
table : orders
+-------+---------------+
| id | created_at |
+-------+---------------+
| 1 | 2018-01-02 |
| 2 | 2018-01-15 |
| 3 | 2018-03-02 |
| 4 | 2018-03-10 |
| 5 | 2018-03-13 |
+-------+---------------+
I want my final results to look like this:
+-------+-----------+----------------------+--------------------------------+
| id | name | recent_sales_count | date_to_start_counting_sales |
+-------+-----------+----------------------+--------------------------------+
| 1 | Apple | 3 | 2018-01-30 |
| 2 | Banana | 0 | 2018-04-09 |
| 3 | Grape | 1 | 2018-03-10 |
+-------+-----------+----------------------+--------------------------------+
So this is what I mean by latest 20 active days for e.g. Apple:
It was last activated at '2018-04-25'. That's 4 days ago.
Before that, it was inactive since '2018-03-15', so all these days until '2018-04-25' don't count.
Before that, it was active since '2018-03-01'. That's more 14 days until '2018-03-15'.
Before that, inactive since '2018-02-01'.
Finally, it was active since '2018-01-01', so it should only count the missing 2 days (4 + 14 + 2 = 20) backwards from '2018-02-01', resulting in date_to_start_counting_sales = '2018-01-30'.
With the '2018-01-30' date in hand, I'm then able to count Apple orders in the last 20 active days: 3.
Hope that makes sense.
Here is a fiddle with the data provided above.

Answer 1

I've got a standard SQL solution, that does not use any window function as you are on MySQL 5
My solution requires 3 stacked views.
It would have been better with a CTE but your version doesn't support it. Same goes for the stacked Views... I don't like to stack views and always try to avoid it, but sometimes you have no other choice, because MySQL doesn't accept subqueries in FROM clause for Views.
CREATE VIEW VIEW_product_dates AS
(
SELECT product_id, created_at AS active_date,
(
SELECT created_at
FROM statuses ti
WHERE name = 'inactive' AND ta.created_at < ti.created_at AND ti.product_id=ta.product_id
GROUP BY product_id
) AS inactive_date
FROM statuses ta
WHERE name = 'active'
);
CREATE VIEW VIEW_product_dates_days AS
(
SELECT product_id, active_date, inactive_date, datediff(IFNULL(inactive_date, SYSDATE()),active_date) AS nb_days
FROM VIEW_product_dates
);
CREATE VIEW VIEW_product_dates_days_cumul AS
(
SELECT product_id, active_date, ifnull(inactive_date,sysdate()) AS inactive_date, nb_days,
IFNULL((SELECT SUM(V2.nb_days) + V1.nb_days
FROM VIEW_product_dates_days V2
WHERE V2.active_date >= IFNULL(V1.inactive_date, SYSDATE()) AND V1.product_id=V2.product_id
),V1.nb_days) AS cumul_days
FROM VIEW_product_dates_days V1
);
The final view produce this :
| product_id | active_date | inactive_date | nb_days | cumul_days |
|------------|----------------------|----------------------|---------|------------|
| 1 | 2018-01-01T00:00:00Z | 2018-02-01T00:00:00Z | 31 | 49 |
| 1 | 2018-03-01T00:00:00Z | 2018-03-15T00:00:00Z | 14 | 18 |
| 1 | 2018-04-25T00:00:00Z | 2018-04-29T11:28:39Z | 4 | 4 |
| 2 | 2018-03-01T00:00:00Z | 2018-04-29T11:28:39Z | 59 | 59 |
| 3 | 2018-03-10T00:00:00Z | 2018-03-15T00:00:00Z | 5 | 5 |
So it aggregates all active periods of all products, it counts the number of days for each period, and the cumulative days of all past active periods since current date.
Then we can query this final view to get the desired date for each product. I set a variable for your 20 days, so you can change that number easily if you want.
SET #cap_days = 20 ;
SELECT PD.id, Pd.name,
SUM(CASE WHEN o.created_at > PD.date_to_start_counting_sales THEN 1 ELSE 0 END) AS recent_sales_count ,
PD.date_to_start_counting_sales
FROM
(
SELECT p.*,
(CASE WHEN LowerCap.max_cumul_days IS NULL
THEN ADDDATE(ifnull(HigherCap.min_inactive_date,sysdate()),(-#cap_days))
ELSE
CASE WHEN LowerCap.max_cumul_days < #cap_days AND HigherCap.min_inactive_date IS NULL
THEN ADDDATE(ifnull(LowerCap.max_inactive_date,sysdate()),(-LowerCap.max_cumul_days))
ELSE ADDDATE(ifnull(HigherCap.min_inactive_date,sysdate()),(LowerCap.max_cumul_days-#cap_days))
END
END) as date_to_start_counting_sales
FROM products P
LEFT JOIN
(
SELECT product_id, MAX(cumul_days) AS max_cumul_days, MAX(inactive_date) AS max_inactive_date
FROM VIEW_product_dates_days_cumul
WHERE cumul_days <= #cap_days
GROUP BY product_id
) LowerCap ON P.id=LowerCap.product_id
LEFT JOIN
(
SELECT product_id, MIN(cumul_days) AS min_cumul_days, MIN(inactive_date) AS min_inactive_date
FROM VIEW_product_dates_days_cumul
WHERE cumul_days > #cap_days
GROUP BY product_id
) HigherCap ON P.id=HigherCap.product_id
) PD
LEFT JOIN items i ON PD.id = i.product_id
LEFT JOIN orders o ON o.id = i.order_id
GROUP BY PD.id, Pd.name, PD.date_to_start_counting_sales
Returns
| id | name | recent_sales_count | date_to_start_counting_sales |
|----|--------|--------------------|------------------------------|
| 1 | Apple | 3 | 2018-01-30T00:00:00Z |
| 2 | Banana | 0 | 2018-04-09T20:43:23Z |
| 3 | Grape | 1 | 2018-03-10T00:00:00Z |
FIDDLE : http://sqlfiddle.com/#!9/804f52/24

Answer 2

Not sure which version of MySql you're working with, but if you can use 8.0, that version came out with a lot of functionality that makes things slightly more doable (CTE's, row_number(), partition, etc.).
My recommendation would be to create a view like in this DB-Fiddle Example, call the view on server side and iterate programatically. There are ways of doing it in SQL, but it'd be a bear to write, test and likely would be less efficient.
Assumptions:
Products cannot be sold during inactive date ranges
Statuses table will always alternate status active/inactive/active for each product. I.e. no date ranges where a certain product is both active and inactive.
View Results:
+------------+-------------+------------+-------------+
| product_id | active_date | end_date | days_active |
+------------+-------------+------------+-------------+
| 1 | 2018-01-01 | 2018-02-01 | 31 |
+------------+-------------+------------+-------------+
| 1 | 2018-03-01 | 2018-03-15 | 14 |
+------------+-------------+------------+-------------+
| 1 | 2018-04-25 | 2018-04-29 | 4 |
+------------+-------------+------------+-------------+
| 2 | 2018-03-01 | 2018-04-29 | 59 |
+------------+-------------+------------+-------------+
| 3 | 2018-03-10 | 2018-03-15 | 5 |
+------------+-------------+------------+-------------+
View:
CREATE OR REPLACE VIEW days_active AS (
WITH active_rn
AS (SELECT *, Row_number()
OVER ( partition BY NAME, product_id
ORDER BY created_at) AS rownum
FROM statuses
WHERE name = 'active'),
inactive_rn
AS (SELECT *, Row_number()
OVER ( partition BY NAME, product_id
ORDER BY created_at) AS rownum
FROM statuses
WHERE name = 'inactive')
SELECT x1.product_id,
x1.created_at AS active_date,
CASE WHEN x2.created_at IS NULL
THEN Curdate()
ELSE x2.created_at
END AS end_date,
CASE WHEN x2.created_at IS NULL
THEN Datediff(Curdate(), x1.created_at)
ELSE Datediff(x2.created_at,x1.created_at)
END AS days_active
FROM active_rn x1
LEFT OUTER JOIN inactive_rn x2
ON x1.rownum = x2.rownum
AND x1.product_id = x2.product_id ORDER BY
x1.product_id);