Traversing the Corporate Ladder: Mastering CTEs for Hierarchical Data in MSSQL 2005

1. Define the CTE:

   WITH EmployeeHierarchy AS (
       -- Anchor member: select each employee as the starting point
       SELECT EmployeeID, EmployeeID AS ManagerID, EmployeeName
       FROM Employees
   
       UNION ALL
   
       -- Recursive member: join with itself to find manager details
       SELECT eh.EmployeeID, e.ManagerID, e.EmployeeName
       FROM EmployeeHierarchy AS eh
       INNER JOIN Employees AS e ON eh.ManagerID = e.EmployeeID
   )
   

2. Explanation:

   • The CTE is named EmployeeHierarchy.

3. Retrieve the data:

   SELECT eh.EmployeeID, eh.EmployeeName, ManagerName = eh2.EmployeeName
   FROM EmployeeHierarchy AS eh
   LEFT JOIN EmployeeHierarchy AS eh2 ON eh.ManagerID = eh2.EmployeeID
   WHERE eh2.EmployeeID IS NOT NULL;
   

   • This query selects desired columns from the EmployeeHierarchy CTE.
   • It performs a LEFT JOIN with the CTE itself, matching eh.ManagerID with eh2.EmployeeID to retrieve the manager's name.
   • The WHERE clause filters out the initial row where eh.ManagerID is null (avoiding self-reference).

This approach allows you to traverse the employee hierarchy in MSSQL 2005 without relying on stored procedures.

• Complexity: Nested CTEs can become intricate, making it challenging to understand and maintain the code. Proper documentation and clear naming conventions are crucial.
• Performance: CTEs can be less performant than stored procedures for complex recursive queries, especially with large datasets. Consider upgrading to a newer SQL Server version for better performance and true recursion capabilities.