All People Report to the Given Manager

All People Report to the Given Manager

What is this problem about?

The "All People Report to the Given Manager interview question" is a SQL/Database challenge that focuses on hierarchical data. You are given a table of employees, where each row contains an employee ID and their direct manager's ID. Your task is to find all employees who report to a specific "Head Manager" (usually ID 1), either directly or indirectly, within a certain number of levels (usually 3).

Why is this asked in interviews?

Amazon and Google ask the "All People Report to the Given Manager coding problem" to evaluate a candidate's ability to handle recursive relationships in a relational database. It tests knowledge of JOIN operations, subqueries, or Recursive Common Table Expressions (CTEs). Hierarchical reporting is a classic real-world data structure, making this a highly practical interview topic.

Algorithmic pattern used

This problem follows the Recursive Query or Multiple Self-Join pattern.

• Self-Join Approach: You join the employee table with itself multiple times.
  • Level 1: Employee -> Manager (where Manager is the Head).
  • Level 2: Employee -> Manager -> Head.
  • Level 3: Employee -> Manager -> Manager -> Head.
• Recursive CTE Approach: You define a base case (direct reports to the Head) and a recursive step (people reporting to those already found) until the desired depth is reached.

Example explanation

Table: Employees(emp_id, manager_id) Data: (2, 1), (3, 2), (4, 3), (7, 1)

• Level 1: Employees 2 and 7 report directly to 1.
• Level 2: Employee 3 reports to 2 (who reports to 1). So 3 reports indirectly to 1.
• Level 3: Employee 4 reports to 3 (who reports to 2, who reports to 1). So 4 reports indirectly to 1. Result: [2, 3, 4, 7]. Note that the Head Manager (ID 1) is usually excluded from the final list.

Common mistakes candidates make

• Hardcoding the Head Manager: Not making the query flexible enough to handle a different manager ID if requested.
• Ignoring the Depth Limit: In some variations, you are asked for all levels; in others, only up to 3. Not reading the constraint can lead to over-engineering.
• Duplicate Results: Using JOIN without UNION or DISTINCT might lead to an employee being listed multiple times if they have multiple paths (though rare in a standard management tree).

Interview preparation tip

Master the "Self-Join" concept in SQL. It's the most common way to represent trees in relational databases. Also, familiarize yourself with WITH RECURSIVE syntax, as it is becoming the standard for solving these types of problems in modern SQL dialects.