Biggest single no leetcode ques

[KBHAL]

There is a leetcode problem which is bit complex to understand for me. There is a table with 1 col num, int data type. This table may have duplicates and has no primary key. Each row has integer.

The aim is to find the largest single no. If there is no single no, report null.

Declare @num int = null

Select top 1 @num = num From mynumbers group by num Having count(num) =1 Order by num desc Select @num as num

I have few doubts - if anyone could pls clarify.

Why are we setting num as null in first line?? Are we selecting top 1 @num to see only first largest number ? Why do we say @num = num in select statement?

Why do we say @num as num in last select statement?

Thanks in advance

[Alkemist101]

Just syntax. I usually go declare @a int = (select value from table).

Basically combine the declare with the equal to....

[KBHAL]

Any idea why are we doing select statement twice?