Sum of sums in different tables

Question

I have problem with SQL query.
I have tableA:

productA priceA  
P1        18  
P2        35  
P1        22  
P2        19  

and also tableB:

productB priceB  
P1        3  
P2        15  
P1        80  
P2        96  

I want as result the sum of two products from the 2 tables.

product price  
P1       123  
P2       165  

I want to sum the sums of the two tables.
I am trying this query but it's wrong.

SELECT productA, 
     (SELECT SUM(priceA) FROM tableA GROUP BY productA), 
     (SELECT SUM(priceB) FROM tableB GROUP BY productB)
FROM tableA, tableB
WHERE productA = productB
GROUP BY productA

Please help me.

Answer 1

You could use a union to merge the tables, and group by on the result:

select  product
,       sum(price)
from    (
        select  productA as product
        ,       priceA as price
        from    TableA
        union all
        select  productB
        ,       priceB
        from    TableB
        ) as SubQueryAlias
group by
        product

Answer 2

This is quite literally the sum of sums:

select
    product,
    sum(price)
from (
    select productA as product, sum(priceA) as price from tableA group by 1
    union all
    select productB, sum(priceB) from tableB group by 1
) 
group by 1