Oracle / MySQL 2WAYS Clean
Oracle\n\nSELECT e.employee_id \n  FROM Employees e \n  LEFT JOIN Salaries s ON e.employee_id = s.employee_id\n  WHERE s.salary IS NULL\n  UNION\n SELECT s1.emp
### Oracle\n```\nSELECT e.employee_id \n  FROM Employees e \n  LEFT JOIN Salaries s ON e.employee_id = s.employee_id\n  WHERE s.salary IS NULL\n  UNION\n SELECT s1.employee_id\n   FROM Salaries s1\n   LEFT JOIN Employees e1 ON e1.employee_id = s1.employee_id\n  WHERE e1.name IS NULL\n```\n\n### MySQL\n\n```\nSELECT employee_id \n  FROM Salaries \n WHERE employee_id NOT IN (SELECT employee_id \n                             FROM Employees\n                           )\nUNION\nSELECT employee_id \n  FROM Employees \n WHERE employee_id NOT IN (SELECT employee_id \n                             FROM Salaries\n                           )\nORDER BY 1\n```
['MySQL', 'Oracle']