EASY SOLUTION USING case
\nSELECT case\n        WHEN e.employee_id is null THEN s.employee_id\n        WHEN s.salary is NULL THEN e.employee_id\n        END AS employee_id\nFROM employe
```\nSELECT case\n        WHEN e.employee_id is null THEN s.employee_id\n        WHEN s.salary is NULL THEN e.employee_id\n        END AS employee_id\nFROM employees e FULL JOIN salaries s ON e.employee_id = s.employee_id\n\nWHERE e.employee_id is null or s.salary is NULL\n\nORDER BY employee_id\n```
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