Call me foolish, but what about the following makes it undesirable? The question didn't ask about a null case of a department with no employees.

-- List employees who have the biggest salary in their departments SELECT em.EmployeeID, em.departmentId, MAX(salary) as salary FROM employees em GROUP BY em.departmentId

In your example, for each row of the result set

* "em.departmentId" will contain one of the distinct values from the "departmentId" column

* "salary" will contain the maximum value of the "salary" column of the table rows whose "departmentId" equals "em.departmentId" of the given result set row.

* "em.EmployeeID" will contain the value of the "EmployeeID" column of one the table rows, whose "departmentID" equals "em.departmentId" of the given result set row, but it is UNDEFINED which one. It IS NOT quaranteed to be the one whose "salary" column equals "MAX(salary)".

See here for examples of how to achieve what is actually needed: http://dev.mysql.com/doc/refman/5.0/en/example-maximum-colum...

As I said, tricky, and, judging from the difficulty level of the other questions, I suspect that the authors of the article have fallen for it themselves.

Thanks for the clarification. 5/6 and dunce hat for me :)

In an interview, it would be wise to mention the special cases that might exist and how you would alter your answer if you had to taken them into account, rather than waiting to be told of the special cases.

I was wondering if the author realized this. Using Microsoft SQL Server, the answer would be to use a window function like row_number or dense_rank and then select where row = 1.