SELECT
    warehouse,
    product, 
    SUM(quantity) qty
FROM
    inventory
GROUP BY
    warehouse,
    product
UNION ALL
SELECT
    warehouse, 
    null,
    SUM(quantity) qty
FROM
    inventory
GROUP BY
    warehouse
UNION ALL
SELECT
    null,
    product, 
    SUM(quantity) qty
FROM
    inventory
GROUP BY
    product
UNION ALL
SELECT
    null,
    null,
    SUM(quantity) qty
FROM
    inventory;
SQL