This version may offer a simplified and faster alternative for you. The inner query for "AllItems" does both a min and max of the last update on a per-item number/sku basis, although I believe they would be one-in-the-same record.
So now, join that results back to the history data by item/sku and only those that match either the min or max date. If a true date/time, there would expect to only be one anyhow, vs just a date-only. So, since there would be 2 possible records (one for the min, one for the max), I am applying a MAX( IIF( )) for each respective matching the minimum and maximum dates respectively and must retain the group by clause.
Note, if you are dealing with date-only entries, or possibilities of the exact same item/sku and lastupdate are the same to the second, then you would need an approach more towards limit 1 per ascending/descending basis.
SELECT
AllItems.ItemNumber,
AllItems.SKU,
AllItems.MinUpdate,
MAX( IIF( rh.lastupdate = AllItems.MinUpdate, rh.Quantity.Sold, 0 )) as QtyAtMinDate,
AllItems.MaxUpdate,
MAX( IIF( rh.lastupdate = AllItems.MaxUpdate, rh.Quantity.Sold, 0 )) as QtyAtMaxDate
from
( SELECT
r.ItemNumber,
r.SKU,
MIN( r.lastupdate ) as MinUpdate,
MAX( r.lastupdate ) as MaxUpdate
FROM
ebx_r_history r
group by
r.ItemNumber,
r.SKU ) AllItems
JOIN ebx_r_history rh
ON AllItems.ItemNumber = rh.ItemNumber
AND AllItems.SKU = rh.SKU
AND ( rh.lastUpdate = AllItems.MinUpdate
OR rh.lastUpdate = AllItems.MaxUpdate )
group by
AllItems.ItemNumber,
AllItems.SKU
Per another answer where you were only looking to IGNORE items within the most recent 14 days, you can just add a WHERE clause to the inner query similar via
WHERE r.LastUpdate >= CURDATE() - INTERVAL 14 DAY
If your history table has an auto-incrementing ID column, AND the respective transactions have the lastUpdate sequentially stamped, such as when they are added and not modified by any other operation, then you could just apply similar but MIN/MAX of the ID column, then join back TWICE on the ID and just each row ONCE such as...
SELECT
AllItems.ItemNumber,
AllItems.SKU,
rhMin.LastUpdate as MinUpdate,
rhMin.QuantitySold as MinSold,
rhMax.LastUpdate as MaxUpdate,
rhMax.QuantitySold as MaxSold
from
( SELECT
r.ItemNumber,
r.SKU,
MIN( r.AutoIncrementColumn ) as MinAutoID,
MAX( r.AutoIncrementColumn ) as MaxAutoID
FROM
ebx_r_history r
group by
r.ItemNumber,
r.SKU ) AllItems
JOIN ebx_r_history rhMin
ON AllItems.MinAutoID = rhMin.AutoIncrementColumn
JOIN ebx_r_history rhMax
ON AllItems.MaxAutoID = rhMax.AutoIncrementColumn
order by
rhMax.LastUpdated