Select Max from each Subset

Question

I'm banging my head here. I feel pretty stupid because I'm sure I've done something like this before, but can't for the life of me remember how. One of those days I guess >.<

Say I have the following data: ---> and a query which returns this: ---> But I want this:

ID   FirstID              ID   FirstID                ID   FirstID
--   -------              --   -------                --   -------
1     1                   1    1                      7    1
2     1                   3    3                      3    3
3     3                   4    4                      6    4
4     4                   5    5                      5    5
5     5
6     4
7     1

Notice that my query returns the records where ID = FirstID, but I want it to return the Max(ID) for each subset of unique FirstID. Sounds simple enough right? That's what I thought, but I keep getting back just record #7. Here's my query (the one that returns the second block of figures above) with some test code to make your life easier. I need this to give me the results in the far right block. It should be noted that this is a self-joining table where FirstID is a foreign key to ID. Thanks :)

declare @MyTable table (ID int, FirstID int)
insert into @MyTable values (1,1),(2,1),(3,3),(4,4),(5,5),(6,4),(7,1)
select ID, FirstID
from @MyTable
where ID = FirstID

Answer 1

Does this work

declare @MyTable table (ID int, FirstID int)
insert into @MyTable values (1,1),(2,1),(3,3),(4,4),(5,5),(6,4),(7,1)

Select FirstID, Max (Id) ID
From @MyTable
Group BY FirstID

Results in

FirstID     ID
----------- -----------
1           7
3           3
4           6
5           5