COALESCE

1
SELECT
2
  customer_name,
3
  COALESCE(phone, email, 'No contact') AS contact
4
FROM customers;

1
SELECT
2
  product_name,
3
  COALESCE(discount, 0) AS discount,
4
  price * (1 - COALESCE(discount, 0) / 100) AS final_price
5
FROM products;

1
SELECT
2
  COALESCE(
3
    preferred_name,
4
    nickname,
5
    first_name || ' ' || last_name,
6
    'Anonymous'
7
  ) AS display_name
8
FROM users;

1
SELECT
2
  p.product_name,
3
  COALESCE(
4
    (SELECT AVG(rating) FROM reviews r WHERE r.product_id = p.id),
5
    0
6
  ) AS avg_rating
7
FROM products p;