MySQL, left join + union
\nselect      e.employee_id\nfrom        employees e\nleft join   salaries s\non          e.employee_id = s.employee_id\nwhere       s.salary is null\n\nUNION\n
```\nselect      e.employee_id\nfrom        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\nfrom        salaries s\nleft join   employees e\non          s.employee_id = e.employee_id\nwhere       e.name is null\n\norder by    1\n```
['Union Find', 'MySQL']