Get count of total employees under each manager (SQL Server) - sql

Question

I need to get, for each of the five people in this table, the total employees reporting to each one of them (either directly or indirectly).
CREATE TABLE employees
([employee] nvarchar(30), [manager] nvarchar(30))
;
INSERT INTO employees
([employee], [manager])
VALUES
('Robert', null),
('Julian', 'Robert'),
('Sophie', 'Robert'),
('Lucy', 'Julian'),
('John', 'Lucy')
;
The output I expect is:
employee
subordinates
Robert
4
Julian
2
Lucy
1
Sophie
0
John
0
I have searched everywhere how to do this type of recursion/hierarchical query, and it seems it is very common to approach this kind of exercise to get the employee hierarchy only (which I managed to do already), but not the total count of employees under each manager.
The best I could get was the following, but it only gets the count for the top manager, while I need it for all employees in the company in a single table (from an answer to this post: SQL Query to get recursive count of employees under each manager).
WITH EmployeeCTE
AS (SELECT e.employee, e.manager as topmanager
FROM employees e, employees m
WHERE e.manager = m.employee AND m.manager IS NULL
UNION ALL
SELECT e.employee, mgr.topmanager
FROM employees e, EmployeeCTE mgr
WHERE e.manager = mgr.employee)
SELECT topmanager, count(*)
FROM EmployeeCTE AS u
GROUP BY topmanager;
Here is a Fiddle to this: http://sqlfiddle.com/#!18/380ba/2

Answer 1

The problem is with getting the zero subordinates for those without subordinates.
One way to get them is via a LEFT JOIN of all employees to the results of the recursive CTE.
WITH CTE_Employees AS (
SELECT employee
FROM employees
GROUP BY employee
)
, RCTE_Managers AS (
SELECT
manager as base_manager
, 1 as depth
, employee
, manager as direct_manager
FROM employees
WHERE manager IS NOT NULL
UNION ALL
SELECT
cte.base_manager
, cte.depth + 1
, emp.employee
, emp.manager
FROM RCTE_Managers cte
JOIN employees emp
ON emp.manager = cte.employee
)
SELECT
emp.employee
, COUNT(DISTINCT mgr.employee) AS subordinates
FROM CTE_Employees emp
LEFT JOIN RCTE_Managers mgr
ON mgr.base_manager = emp.employee
GROUP BY emp.employee
ORDER BY COUNT(mgr.employee) DESC, emp.employee;
employee
subordinates
Robert
4
Julian
2
Lucy
1
John
0
Sophie
0
Test on db<>fiddle here