176. Second Highest Salary.tsql

with RankedSalaries as (
    select
        *
        , dense_rank() over (order by salary desc) as rank
    from Employee
)
select
    (case
        when exists(select rank from RankedSalaries where rank = 2) then (select top(1) salary from RankedSalaries where rank = 2)
        else null
    end) as SecondHighestSalary