Drill 12: Explain each line — Debugging queries

CREATE TABLE orders (
  id SERIAL PRIMARY KEY,
  customer TEXT NOT NULL,
  total NUMERIC(10, 2) NOT NULL,
  status TEXT
);

SELECT id, customer, total
FROM orders
WHERE total > 100
LIMIT 20;

EXPLAIN SELECT * FROM orders WHERE customer = 'Ada';

SELECT customer, COUNT(*)
FROM orders
GROUP BY customer
HAVING COUNT(*) > 1;

SELECT id, customer, status
FROM orders
WHERE status IS NULL;