这项工作

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

结果

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