Are all 3 of these fields indexed? Are they unique? Are they unique to each other? Is it *possible* for a barcode to belong to multiple products?
How about three select queries tied together with a union?
Something like:
Code:
SELECT Products.ID, Quantity FROM Products INNER JOIN [Scan Data] ON [Scan Data].[Part #] = Products.[Product Number]
WHERE [Scan Data].[Scan Date] = #8/21/2018#
UNION
SELECT Products.ID, Quantity FROM Products INNER JOIN [Scan Data] ON [Scan Data].[Part #] = Products.[MFG Number]
WHERE [Scan Data].[Scan Date] = #8/21/2018#
UNION
SELECT Products.ID, Quantity FROM Products INNER JOIN [Scan Data] ON [Scan Data].[Part #] = Products.[ALT Number]
WHERE [Scan Data].[Scan Date] = #8/21/2018#
And then run an aggregate query on the union query.