UNION + WHERE NOT IN ()
\nSELECT employee_id FROM Employees WHERE employee_id NOT IN (SELECT employee_id FROM Salaries)\nUNION \nSELECT employee_id FROM Salaries WHERE employee_id NOT 
```\nSELECT employee_id FROM Employees WHERE employee_id NOT IN (SELECT employee_id FROM Salaries)\nUNION \nSELECT employee_id FROM Salaries WHERE employee_id NOT IN (SELECT employee_id FROM Employees)\n\nORDER BY 1 ASC\n```
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