如何选择在项目上工作时间最长的员工

Question

In the following table I found the two projects that are over budget but I must find the employee number of the person that worked the most hours on each project:

+------------+-----------+----------------+-------------+
| Department | ProjectID | EmployeeNumber | HoursWorked |
+------------+-----------+----------------+-------------+
| Marketing  |      1000 |              1 |       30.00 |
| Marketing  |      1300 |              1 |       35.00 |
+------------+-----------+----------------+-------------+

The correct employeenumber should be 8 for both projects and 75 and 80 hours.

Any idea how to retrieve the MAX hours worked for these individual projects?

Answer 1

The easy way is like this:

select * from (
    select ProjectID, EmployeeNumber
    from assignment
    group by 1, 2
    order by sum(HoursWorked) desc
) x
group by 1

See live demo on SQLFiddle.

This works due to mysql's special handling of group by, which allows not all non-aggregate columns to be listed and in such cases returns just the first row encountered for each group.