The following data definition defines an organization's employee hierarchy. An employee is a manager if any other employee has their managerId set to the first employees id. An employee who is a manager may or may not also have a manager. TABLE employees id INTEGER NOT NULL PRIMARY KEY managerId INTEGER REFERENCES employees(id) name VARCHAR(30) …

workers.sql

SELECT name FROM employees
WHERE id NOT IN (SELECT managerId FROM employees WHERE managerId IS NOT NULL);

CREATE TABLE employees (
id INTEGER NOT NULL PRIMARY KEY,
managerId INTEGER REFERENCES employees(id),
name VARCHAR(30) NOT NULL
);

INSERT INTO employees(id, managerId, name) VALUES(1, NULL, 'John');
INSERT INTO employees(id, managerId, name) VALUES(2, 1, 'Mike');

-- Expected output (in any order):
-- name

---

-- Mike

-- Explanation:
-- In this example.
-- John is Mike's manager. Mike does not manage anyone.
-- Mike is the only employee who does not manage anyone.