dueify/mysql-fiddling

-- Example case create statement:
CREATE TABLE customers (
  id INTEGER PRIMARY KEY NOT NULL,
  name VARCHAR(50),
  balance DECIMAL(10,2));

CREATE TABLE orders (
  id INTEGER PRIMARY KEY NOT NULL,
  customerId INTEGER NOT NULL REFERENCES customers(id),
  product VARCHAR(100));

INSERT INTO customers(id, name, balance) VALUES(1, 'ACME', 500);
INSERT INTO orders(id, customerId, product) VALUES(1, 1, 'Diamond blade');

INSERT INTO customers(id, name, balance) VALUES(2, 'Doolittle Co.', -100);
INSERT INTO orders(id, customerId, product) VALUES(2, 2, 'Vacuum cleaner');

-- Insert answer here

SELECT * FROM orders WHERE customerId IN
(SELECT id FROM customers WHERE balance > 0)

-- OR TO DELETE

DELETE FROM orders WHERE customerId IN
(SELECT id FROM customers WHERE balance < 0)

-- Expected output (in any order):
-- id    customerId    product
-- ---------------------------------
-- 1     1             Diamond blade

-- Explanation:
-- In this example.
-- A diamond blade was ordered by ACME. As ACME has a positive balance, this order shouldn't be deleted.
-- A vacuum cleaner was ordered by Doolittle Co. As Doolittle Co. has a negative balance, the order should be deleted.