All three solutions - last one is epic
Solution 1\n\nSELECT employee_id from Employees e WHERE employee_id not in (Select employee_id from Salaries)\nUNION \nSELECT employee_id from Salaries s WHERE 
Solution 1\n```\nSELECT employee_id from Employees e WHERE employee_id not in (Select employee_id from Salaries)\nUNION \nSELECT employee_id from Salaries s WHERE employee_id not in (Select employee_id from Employees)\nORDER BY employee_id;\n```\n\n\nSolution 2\n```\nSelect e.employee_id from Employees e \nLEFT JOIN Salaries s \nON e.employee_id = s.employee_id\nWHERE s.salary  is NULL\n\nUNION\n\nSelect s.employee_id from Salaries s\nLEFT JOIN Employees e \nON e.employee_id = s.employee_id\nWHERE e.name is NULL\n\nORDER BY employee_id;\n```\n\nSolution 3 (epic)\n```\nselect T.employee_id from\n\n(select * from Employees\nunion\nselect * from Salaries\n) as T\n\ngroup by T.employee_id\n\nhaving count(T.employee_id) < 2\n\norder by T.employee_id asc\n\n```
['MySQL']