Selecting one vs all records within group in SQL Server

Question

I have a table in SQL Server something like this (these records are coming from user input later I have to join this table with business table)

Table A

id	group	item
1	A	4567876
2	A	5678988
3	A	9999999
4	B	1234567
5	B	6846677

For each group I want to select, If there is any entry for item 9999999 then select only this record else all records in that respective group. (e.g for given example in group A select item 9999999 and for group B all items)

id	group	item
3	A	9999999
4	B	1234567
5	B	6846677

I don't want to delete any records from the table.

Answer 1

You can use not exists:

select a.*
from a
where a.item = 9999999 or
      not exists (select 1
                  from a a2
                  where a2.group = a.group and
                        a2.item = 9999999
                 );

You can also use a fancy trick with rank():

select top (1) with ties t.*
from t
order by rank() over (partition by group
                      order by (case when item = 9999999 then 1 else 2 end)
                     );