SQL #1

not_manager_employees.sql

-- Workers
-- 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) NOT NULL
-- Write a query that selects the names of employees who are not managers.
SELECT * 
FROM employees 
WHERE id IN (SELECT id FROM employees WHERE managerId IS NULL)