MySql & Oracle sql solution || UNION || NOT IN
MySQL/Oracle sql solution\n\nSELECT employee_id\nFROM Employees\nWHERE employee_id NOT IN (SELECT employee_id\n                          FROM Salaries)\nUNION\n
MySQL/Oracle sql solution\n```\nSELECT employee_id\nFROM Employees\nWHERE employee_id NOT IN (SELECT employee_id\n                          FROM Salaries)\nUNION\nSELECT employee_id\nFROM Salaries\nWHERE employee_id NOT IN (SELECT employee_id\n                          FROM Employees)\nORDER BY employee_id;\n```
['MySQL', 'Oracle']