SQLite UNION ALL and Group by

Question

with this query I want to select all data from two different tables, grouping the identical data of the fields of the 2 tables. The query works in part, because it groups the data of the tables, but does not group them all together. See code and image

            SELECT product,
            product_modified,
            amount, 
            SUM(quantity) AS q FROM bills_stored     
            GROUP BY product

            UNION ALL

            SELECT product, 
            product_modified, 
            product_amount, 
            SUM(quantity) AS q FROM ordering 
            GROUP BY product ORDER BY q DESC

Answer 1

You should first take the union, and then aggregate:

SELECT
    product,
    SUM(quantity) AS q
FROM
(
    SELECT product, quantity FROM bills_stored
    UNION ALL
    SELECT product, quantity FROM ordering
) t
GROUP BY product;

Note that if you also want to select the product_modified column then rightfully it should also appear in the GROUP BY clause.