Perform Conditional Updates on Multiple Columns

UPDATE products
SET
    price = CASE
        WHEN category = 'Electronics' THEN price * 1.05
        WHEN category = 'Books' THEN price * 1.02
        ELSE price
    END,
    stock = CASE
        WHEN category = 'Electronics' THEN stock - 10
        WHEN category = 'Books' THEN stock - 5
        ELSE stock
    END,
    last_updated = NOW()
WHERE is_active = TRUE;

How it works: This query performs a conditional update on the `products` table. It uses `CASE` expressions within the `SET` clause to apply different price and stock adjustments based on the `category` of each product. For example, 'Electronics' receive a 5% price increase and 10 units reduction in stock, while 'Books' get a 2% price increase and 5 units reduction. The `last_updated` timestamp is also updated for all active products.