Traducir a SQL no es tan difícil, pero el rendimiento puede ser malo. Esto le dará la marca de tiempo cuando el producto volvió a estar disponible:
SELECT inv.*,
( SELECT MIN(`inv2`.`in_stock_at`)
FROM inventories AS inv2
WHERE inv2.`product_id` = inv.`product_id` -- same product
AND inv2.`pusher_id` = `inv`.`pusher_id` -- same pusher
AND `inv2`.`created_at` > inv.`created_at` -- later timestamp
AND `inv2`.`item_count` > 0 -- in stock
) AS inStockAgain_at
from `inventories` AS inv
WHERE inv.`item_count` <= 0 -- out of stock
-- AND inv.`product_id`=9
Editar:
Eliminar filas consecutivas con stock cero es más complicado:
SELECT inv.*, dt.inStockAgain_at
FROM inventories AS inv
JOIN
(
SELECT product_id, pusher_id,
MIN(created_at) AS min_created_at,
inStockAgain_at
FROM
(
SELECT product_id, pusher_id, created_at,
( SELECT MIN(inv2.created_at)
FROM inventories AS inv2
WHERE inv2.product_id = inv.product_id -- same product
AND inv2.pusher_id = inv.pusher_id -- same pusher
AND inv2.created_at > inv.created_at -- later timestamp
AND inv2.item_count > 0 -- in stock
) AS inStockAgain_at
FROM inventories AS inv
WHERE inv.item_count <= 0
) AS dt
GROUP BY product_id, pusher_id, inStockAgain_at
) AS dt
ON inv.product_id = dt.product_id
AND inv.pusher_id = dt.pusher_id
AND inv.created_at = dt.min_created_at
Ver fiddle
