MySQL: SUM() on Self-Joined table - mysql

Question

I have the following table named Stock_Level. (It has around 200,000 rows)
| sku | location_id | stock_level | allocated | on_order | date_booked_in | date_last_sold | date_last_stock_take| status_since |
|-----|-------------|-------------|-----------|----------|---------------------|---------------------|---------------------|---------------------|
| 1 | 1 | 100 | 2 | 15 | 2020-12-01 12:34:00 | 2020-11-25 12:34:00 | 2021-01-01 12:00:00 | 2021-02-09 12:55:00 |
| 2 | 1 | 50 | 1 | 0 | 2020-11-02 12:34:00 | 2020-10-09 12:34:00 | 2021-01-01 12:00:00 | 2021-02-09 12:55:00 |
| 3 | 1 | 10 | 0 | 12 | 2020-08-05 12:34:00 | 2020-05-04 12:34:00 | 2021-01-01 12:00:00 | 2021-02-09 12:55:00 |
| 1 | 2 | 80 | 0 | 13 | 2020-09-09 12:34:00 | 2020-12-06 12:34:00 | 2021-01-03 12:00:00 | 2021-02-09 13:55:00 |
| 2 | 2 | 35 | 3 | 0 | 2020-07-10 12:34:00 | 2020-08-05 12:34:00 | 2021-01-03 12:00:00 | 2021-02-09 12:55:00 |
| 1 | 3 | 60 | 1 | 0 | 2020-08-12 12:34:00 | 2020-09-04 12:34:00 | 2021-02-03 12:00:00 | 2021-02-09 12:55:00 |
| 2 | 3 | 9 | 0 | 17 | 2020-05-30 12:34:00 | 2020-01-01 12:34:00 | 2021-02-03 12:00:00 | 2021-02-09 12:55:00 |
PRIMARY key is on sku and location_id
There is also an INDEX on status_since
A SKU can be in multiple locations. When an item is booked in, sold or stock taken, status_since is updated to NOW()
What I'm trying to do
I have a script that runs every 15 minutes, selecting items that have been updated in the last 15 minutes, with the SUM of (stock_level - allocated) for that sku, along with the total number on order and the MAX() values of date_booked_in, date_last_sold and date_last_stock_take
The code that I've currently got is this:
SELECT sku,
SUM(stock_level - allocated) AS available,
SUM(on_order) AS on_order,
MAX(date_booked_in) AS date_booked_in,
MAX(date_last_sold) AS date_last_sold,
MAX(date_last_stock) AS date_last_stock
FROM Stock_Level
WHERE
sku IN(
SELECT sku
FROM Stock_Level
WHERE
status_since>= DATE_SUB(NOW(), INTERVAL 15 MINUTE)
AND status_since<= NOW()
)
GROUP BY sku
This works fine when there are only a few items that have been recently updated; however sometimes many hundreds can be updated within a 15 minute period, and this query grinds to a halt.
I suspect there is a way to do this with a self join rather than using an IN() clause but I can't for the life of me work it out.
What would be some potential ways to rewrite this query?

Answer 1

You can use EXISTS which is much faster than IN and is always recommended:
SELECT sku,
SUM(stock_level - allocated) AS available,
SUM(on_order) AS on_order,
MAX(date_booked_in) AS date_booked_in,
MAX(date_last_sold) AS date_last_sold,
MAX(date_last_stock) AS date_last_stock
FROM Stock_Level
WHERE
EXISTS(
SELECT 1
FROM Stock_Level sl2
WHERE
sl2.status_since>= DATE_SUB(NOW(), INTERVAL 15 MINUTE)
AND sl2.status_since<= NOW()
AND sku.sku = sl2.sku
)
GROUP BY sku