Question

Let’s say I have two tables with identical structure, call them A & B. The only columns of concern for this issue are product_type, price, and volume.

Each combination of product_type & price may be repeated multiple times in each table with varying volumes. I’m trying to find instances of a combination having a different TOTAL volume in one table than the other.

This would include when a combination from table A is not represented in Table B whatsoever, or vice-versa.

===================

Example:

Table A:

ID   Product_type   Price  Volume
---  ------------   -----  ------
1         X           $1     10
2         X           $1     11
3         Z           $2     10

Table B:

ID   Product_type   Price  Volume
--   -------------  -----  -------
1         X           $1     21
2         Y           $1     5
3         Z           $2     7
4         Z           $2     4

Notice that sum of volumes of X @ $1 in Table A is 21, which matches Table B.
Y @ $1 is present in Table B, but not in A.
Z @ $2 is present in both tables but the sums of their volumes differ. I would like the query to return each product_type and price combination that breaks the rules (i.e. Y @ $1 and Z @ $2).

I’ve tried using GROUP, UNION, DISTINCT, sub-queries and various combinations of the above but can’t seem to figure it out.

Answer 1

create table a (ID integer, Product_type char(1), Price float, Volume integer);
create table b (ID integer, Product_type char(1), Price float, Volume integer);

insert into a (ID, Product_type, Price, Volume) values
(1, 'X', 1, 10),
(2, 'X', 1, 11),
(3, 'Z', 2, 10)
;
insert into b (ID, Product_type, Price, Volume) values
(1, 'X', 1, 21),
(2, 'Y', 1, 5),
(3, 'Z', 2, 7),
(4, 'Z', 2, 4)
;

select 
    a.Product_type as Product_type_a,
    a.Price as Price_a,
    a.Volume as Volume_a,
    b.Product_type as Product_type_b,
    b.Price as Price_b,
    b.Volume as Volume_b
from (
        select Product_type, Price, sum(Volume) as Volume
        from a
        group by Product_type, Price
    ) a
    full outer join (
        select Product_type, Price, sum(Volume) as Volume
        from b
        group by Product_type, Price
    ) b on a.Product_type = b.Product_type and a.Price = b.Price
where 
    a.Volume != b.Volume
    or a.Volume is null or b.Volume is null
;
 product_type_a | price_a | volume_a | product_type_b | price_b | volume_b 
----------------+---------+----------+----------------+---------+----------
 Z              |       2 |       10 | Z              |       2 |       11
                |         |          | Y              |       1 |        5