UPDATE Statement

-- Update a single product's price
UPDATE products SET price = 899.99 WHERE id = 1;

-- Update multiple columns at once
UPDATE products
SET price = 549.99, stock = 100
WHERE name = 'Phone';

-- Update using an expression (10% price increase for all)
UPDATE products SET price = price * 1.10;
-- WARNING: no WHERE — updates ALL products!

-- Update order status
UPDATE orders SET status = 'shipped' WHERE id = 2;

-- Update only if condition met
UPDATE products SET stock = 0 WHERE stock < 5;

-- PostgreSQL: RETURNING shows what changed
UPDATE orders
SET status = 'delivered'
WHERE id = 1
RETURNING id, status, total_amount;

-- Conditional update with CASE
UPDATE products
SET price = CASE
  WHEN price > 500 THEN price * 0.95   -- 5% off expensive items
  ELSE price * 0.90                    -- 10% off cheaper items
END;