Question

The actual tables..

The top left is the assembly table

The top right is the items_table

the bottom left is the inventory table

I wanted to update the inventory based on the orders..

each product has multiple inventory items and I need to multiple each quantity in assembly_table by the quantity in items_table

Answer 1

You could join the tables together to multiply quantities with the same product_tuid:

select  a.product_tuid
,       a.quantity * i.quantity as QuantityProduct
from    assembly_table a
inner join
        items_table i
on      i.product_tuid= a.product_tuid