SQL Server - Issues with Recursive Common Table Expressions Returning Incorrect Row Counts
I'm currently working with SQL Server 2019, and I've implemented a recursive Common Table Expression (CTE) to generate a hierarchy of employee records. However, I'm encountering unexpected row counts when querying the results, which seems to be caused by duplicate entries in the hierarchy. Here's the simplified structure of my Employee table: ```sql CREATE TABLE Employees ( EmployeeID INT PRIMARY KEY, Name NVARCHAR(100), ManagerID INT, FOREIGN KEY (ManagerID) REFERENCES Employees(EmployeeID) ); ``` The recursive CTE I'm using looks like this: ```sql WITH EmployeeHierarchy AS ( SELECT EmployeeID, Name, ManagerID, 0 AS Level FROM Employees WHERE ManagerID IS NULL -- Start with top-level employees UNION ALL SELECT e.EmployeeID, e.Name, e.ManagerID, eh.Level + 1 FROM Employees e INNER JOIN EmployeeHierarchy eh ON e.ManagerID = eh.EmployeeID ) SELECT * FROM EmployeeHierarchy; ``` When executing this query, I expected to see a well-structured hierarchy, but instead, I'm getting several duplicate entries for some employees. For instance, if an employee has two managers (which should not occur due to the foreign key constraint), the CTE is not filtering them out effectively, leading to inflated row counts. I've tried adding a `DISTINCT` clause around the final SELECT statement: ```sql SELECT DISTINCT * FROM EmployeeHierarchy; ``` But this doesn't seem to resolve the issue completely, as some duplicates still appear depending on the data. Additionally, I verified that the data integrity is intact and that no employees have multiple managers, which leads me to believe there might be some issue with how the recursion is being handled. Does anyone have insights on why my recursive CTE is returning these duplicate rows, or how I might be able to refine my query to ensure it only returns unique entries? Any help or suggestions would be greatly appreciated. I recently upgraded to Sql 3.11. This issue appeared after updating to Sql latest. Is there a simpler solution I'm overlooking?