Advanced SQL, Problem 28

--Problem 28.
--Write a SQL query to display the number of managers from each town.

SELECT
    Managers.TownName AS Town,
    COUNT(Managers.managerId) AS [NUMBER OF managers]
FROM (SELECT DISTINCT
    e.EmployeeID AS managerId,
    t.Name AS TownName
FROM Employees e
JOIN Employees m
    ON e.EmployeeID = m.ManagerID
JOIN Addresses a
    ON a.AddressID = e.AddressID
JOIN Towns t
    ON t.TownID = a.TownID) AS Managers
GROUP BY Managers.TownName