Circular Dependency Check

In a healthy corporate hierarchy, the reporting structure should form a directed acyclic graph (DAG). However, data entry errors can lead to circular dependencies—where Employee A reports to Employee B, who reports to Employee C, who eventually reports back to Employee A.

Write a query to identify all employees who are part of such a circular chain. An employee is considered part of a circular dependency if they appear anywhere within a reporting loop.

Rules:

• Output column: employee_id.
• Result must be sorted in ascending order.
• A circular dependency can involve any number of employees (minimum 2).
• The top-level CEO typically has a null manager_id, but in a cycle, no one may have a null manager_id in that specific loop.