SELECT product, quantity, price, (quantity * price) AS total_cost FROM df

SELECT product, quantity, price, (quantity * price) * CASE WHEN product = 'Electronics' THEN 0.9 WHEN product = 'Groceries' THEN 0.8 ELSE 1 END AS total_cost FROM df

SELECT product, quantity, price, (quantity * price) * CASE WHEN product IN ('Electronics', 'Groceries') THEN 0.8 ELSE 1 END AS total_cost FROM df

SELECT product, quantity, price, SUM(quantity * price) * CASE WHEN product = 'Electronics' THEN 0.9 WHEN product = 'Groceries' THEN 0.8 ELSE 1 END AS total_cost FROM df GROUP BY product

SELECT product, quantity, price, (quantity * price) * CASE WHEN product = 'Electronics' THEN 0.9 WHEN product = 'Groceries' THEN 0.8 ELSE 1 END AS total_cost FROM df UNION ALL SELECT product, quantity, price, (quantity * price) AS total_cost FROM df WHERE product NOT IN ('Electronics', 'Groceries')