Calculate stock from two transaction tables to a third one in MySQL -

i have 2 tables, 1 incoming shipments , 1 outgoing. there lot of stock queries in various groupings , need fast, i'd create third table summing above 2 , run queries on that. possible using sql only?

simplified example:

table: incoming id  productid  amount_in ------------------------ 1   6          100 2   5          300 3   6           50 4   2           10  table: outgoing id  productid  amount_out ------------------------- 1   5          10 2   5          20 3   6          30 

resulting table should contain remaining stock:

table: stock productid  amount --------------------- 2          10 5          270   -- 300-10-20 6          120   -- 100+50-30 

i have grouped 2 tables using union all, preserve similar records, used insert select statement obtained table inserting product id , sum of amount, multiply amount_out -1 subtract in sum.

insert stock  select productid, sum(amount) from(         select productid , amount_in amount incoming          union          select productid , amount_out * -1 amount outgoing) group productid