NVL

1
SELECT
2
  customer_name,
3
  NVL(phone, 'No Phone') as phone,
4
  NVL(email, 'No Email') as email
5
FROM customers;

1
SELECT
2
  product_name,
3
  price,
4
  discount_percent,
5
  price * (1 - NVL(discount_percent, 0) / 100) as final_price
6
FROM products;

1
SELECT
2
  department,
3
  SUM(NVL(bonus, 0)) as total_bonus,
4
  AVG(NVL(bonus, 0)) as avg_bonus
5
FROM employees
6
GROUP BY department;