SQL Server 2019: Why Is My CTE Returning Unexpected Row Counts After Recursive Call?
I've been researching this but I'm learning this framework and I tried several approaches but none seem to work. Hey everyone, I'm running into an issue that's driving me crazy. I'm stuck on something that should probably be simple. I'm encountering an issue with a Common Table Expression (CTE) that is supposed to recursively gather hierarchical data from my SQL Server 2019 database, but I'm getting unexpected row counts. The structure involves a simple hierarchy of employees and their managers stored in a table called `Employees`, which has the following schema: ```sql CREATE TABLE Employees ( EmployeeID INT PRIMARY KEY, EmployeeName NVARCHAR(100), ManagerID INT NULL, FOREIGN KEY (ManagerID) REFERENCES Employees(EmployeeID) ); ``` I am trying to fetch all employees under a specific manager, including those at multiple levels below. Here is the CTE I've written: ```sql WITH RecursiveCTE AS ( SELECT EmployeeID, EmployeeName, ManagerID FROM Employees WHERE ManagerID = @ManagerID UNION ALL SELECT e.EmployeeID, e.EmployeeName, e.ManagerID FROM Employees e INNER JOIN RecursiveCTE r ON e.ManagerID = r.EmployeeID ) SELECT * FROM RecursiveCTE; ``` When I run this query with a specific `@ManagerID`, I expect to see all related employees. However, I'm noticing that the CTE sometimes returns duplicate rows or omits certain employees. I've checked the hierarchy manually and confirmed that there are no circular references in the data. I've also tried adding a distinct clause to the final select: ```sql SELECT DISTINCT * FROM RecursiveCTE; ``` But that didn't resolve the issue. The duplicates still appear, and in some cases, I'm missing employees who should be included in the result set. Additionally, I checked the execution plan and saw that SQL Server opts for a nested loop join during the recursion. Could this have an impact on performance or the integrity of the data returned? Is there something Iām missing in how CTEs handle recursion, or is there a more reliable way to implement this that prevents these issues? I'm working on a service that needs to handle this. I'd really appreciate any guidance on this. For context: I'm using Sql on Windows. My team is using Sql for this mobile app. I'm working with Sql in a Docker container on Windows 10. This issue appeared after updating to Sql 3.9. Could someone point me to the right documentation? The project is a REST API built with Sql. I'd be grateful for any help. My development environment is Ubuntu 22.04. Has anyone dealt with something similar? The stack includes Sql and several other technologies. Any suggestions would be helpful.