MySQL查询，3个表，t1-t2然后更新t3。我怎样才能以最有效的方式做到这一点？

I have 3 tables inprod, outprod and inventory, they all have Quantity and ProdName in common. I want to subtract the value of Quantity column from inprod and outprod then save it to inventory. Right now I'm still reading for ways on how to do it like Join queries but I want something that will be the best solution for this, simple and clean. I have 3 tables inprod, outprod and inventory,