Recursive CTE Employee Hierarchy Query – Sql Null 2

You are an expert SQL developer specializing in complex hierarchical queries. Using the information below, create a complete, production‑ready solution that retrieves an employee hierarchy with a recursive Common Table Expression (CTE). Follow each requirement precisely and present the answer in the exact output format specified.

Database schema

CREATE TABLE employees (
    employee_id   INT PRIMARY KEY,
    employee_name VARCHAR(100) NOT NULL,
    manager_id    INT NULL,               -- references employees.employee_id
    hire_date     DATE NOT NULL,
    salary        DECIMAL(12,2) NOT NULL,
    department_id INT NOT NULL
);

• manager_id is NULL for top‑level executives.
• The table may contain cycles (e.g., erroneous manager references) and employees with missing managers (orphaned rows).

Task

1. Write a single, self‑contained SQL script that:

   • Detects and prevents infinite loops caused by cycles.
   • Returns the full hierarchy for all employees, even if they are orphaned.
   • Includes the following columns in the result set:
     • employee_id
     • employee_name
     • manager_id
     • hierarchy_level (0 for top‑level, 1 for direct reports, etc.)
     • path (a slash‑separated string of employee_ids from the root to the current employee, e.g., 1/4/7)
     • total_subordinates (the count of all direct and indirect reports under each employee)
   • Orders the final result by path.

2. Provide inline comments within the SQL script explaining each major step, especially how cycle detection works.

3. After the script, include a brief explanation (≈150‑200 words) covering:

   • How the recursive CTE builds the hierarchy.
   • The technique used to break cycles.
   • Any assumptions made (e.g., maximum depth).

4. Supply sample data (5‑7 rows) that illustrates:

   • A normal hierarchy.
   • At least one cycle.
   • At least one orphaned employee. Show the INSERT statements and the expected output of the query when run against this sample data (present the output as a markdown table).

5. Recommend performance‑enhancing indexes (including index definitions) that would optimize the recursive query for a large employees table.

Output format

1. SQL Script – enclosed in a markdown code block with language tag sql.
2. Explanation – a separate markdown paragraph titled Explanation.
3. Sample Data – markdown code block with INSERT statements (language sql), followed by a markdown table titled Expected Output.
4. Index Recommendations – markdown code block (language sql) listing each CREATE INDEX statement, preceded by a brief bullet list of why each index is useful.

Deliver exactly these sections in the order listed, with no extra commentary or headings beyond those specified.