only 1 value returns with sql query - sql-server

Question

AdventureWorks2012 DB - I am trying to return top 1 or 2 emlpoyees from Finance dept and Engineer dept who have worked longest. I cant get my query to return both, only results from engineering show. Any suggestions?
SELECT TOP 2 EDH.StartDate, E.BusinessEntityID, D.Name, EDH.EndDate, DATEDIFF(hour,EDH.StartDate, GETDATE()) AS HoursWorked
FROM HumanResources.Employee E
INNER JOIN Person.Person PP ON E.BusinessEntityID = PP.BusinessEntityID
INNER JOIN HumanResources.EmployeeDepartmentHistory EDH ON E.BusinessEntityID = EDH.BusinessEntityID
INNER JOIN HumanResources.Department D ON D.DepartmentID = EDH.DepartmentID
WHERE (D.Name LIKE 'Finance' OR D.Name = 'Engineering')
AND EDH.EndDate IS NULL
GROUP BY D.Name, EDH.StartDate,E.BusinessEntityID,EDH.EndDate
ORDER BY EDH.StartDate ASC

Answer 1

Your problem is that the employees from Engineering happen to have started before the employees from Finance. The ORDER BY is affecting all of your records (both departments), and then the TOP 2 value is grabbing the two most recent employees, regardless of departments.
If you are trying to write a query that returns the first employee from each department, you're going to have to get a bit more complex. Here is an example that uses the ROW_NUMBER() function to order employees within each department by their start date, then filters those records to only return employees who are the first individuals in their department.
SELECT
StartDate,
BusinessEntityID,
Name,
EndDate,
HoursWorked
FROM
(
SELECT
EDH.StartDate,
E.BusinessEntityID,
D.Name,
EDH.EndDate,
DATEDIFF(hour,EDH.StartDate, GETDATE()) AS HoursWorked,
ROW_NUMBER() OVER (PARTITION BY D.Name ORDER BY EDH.StartDate) AS RowNumberWithinDepartment
FROM
HumanResources.Employee E
INNER JOIN
Person.Person PP ON E.BusinessEntityID = PP.BusinessEntityID
INNER JOIN
HumanResources.EmployeeDepartmentHistory EDH ON E.BusinessEntityID = EDH.BusinessEntityID
INNER JOIN
HumanResources.Department D ON D.DepartmentID = EDH.DepartmentID
WHERE
(D.Name LIKE 'Finance' OR D.Name = 'Engineering') AND
EDH.EndDate IS NULL
GROUP BY D.Name, EDH.StartDate,E.BusinessEntityID,EDH.EndDate
) x
WHERE RowNumberWithinDepartment = 1
ORDER BY StartDate ASC