IN statement transition - sql

Question

Using a subquery list all male employees with salaries higher than any female employee. Does this look right? Also I need to change it to an IN statement. Everything I've tried returns all female salaries.
SELECT FirstName, LastName, Salary
FROM Employee
WHERE Salary > ALL
(Select Salary FROM Employee
WHERE Gender = 'F')

Answer 1

Right, for the record, I think Gordon's answer is technically much better than what follows. He's doing it right. The requirement to use IN is frankly bizarre.
Since x > ALL y is naturally translated to a NOT EXISTS y such that x <= y
and EXISTS can relatively naturally be translated to IN, we could do this as x NOT IN (z such that z <= y). Assuming the Employee table has a PK field called EmployeeID, you can do this as follows (I threw in some bonus INs for you for free):
SELECT
m.FirstName,
m.LastName,
m.Salary
FROM
Employee m
WHERE
m.Gender IN ('M')
AND m.Salary is not null
AND m.EmployeeID NOT IN
(
select m2.EmployeeID
from Employee m2
where m2.Salary <= (select f.Salary
FROM Employee f
where f.Gender IN ('F'))
)
AND 'Why' IN ('Why','IN','Why','?')
AND 'Why' NOT IN ('Another','Way','?')
This is horrid and much less efficient than Gordon's answer.
If this is part of an assignment for a course, one has to wonder what the person setting this assignment was thinking. There's the obvious possibility that they simply don't know what they are doing, but perhaps they wanted you to jump through some logical hoops or to teach you that it's often possible to achieve the same thing in multiple different ways and that these may or may not be equally efficient.

Answer 2

First, I would write this as:
SELECT m.*
FROM Employee m
WHERE m.Gender = 'M' AND
m.Salary > (SELECT MAX(f.Salary)
FROM Employee f
WHERE f.Gender = 'F'
);
I like this version because it is quite explicit. It is almost a direct translation of "Get all males that earn more than the highest paid female."
Your version also works, under the assumption that gender only takes on two values. However, it relies on subtlety: The comparison is >. So, no female can have a salary higher than all females (including herself). Hence, the outer query can only return not-females, which happen to be males.
Instead of going through those mental gymnastics, the condition on = 'M' makes the intention of the query much clearer.
With that condition, the query is clearer:
SELECT m.*
FROM Employee m
WHERE m.Gender = 'M' AND
m.Salary > ALL (SELECT f.Salary
FROM Employee f
WHERE f.Gender = 'F'
);
I should note that this version is better than the version with MAX() in one edge case. When there are no females, this will return all employees. The version with MAX() will return no rows at all.
I should add: It is not obvious how to turn this query into a version using IN, at least in a sensible way.