get records within same group and with condition

I have a table with following record.

ParentID Value
1 NULL
1 NULL
2 3
2 NULL
3 4
3 10

How to write a query to get records with same parentID and at least one value is NULL and NON Null..

For example, returned record should be
ParentID Value
2 3
2 NULL

Not clear, can you explain it further. 34 and 310 have same parent 3, why is that not in result?

Because the record has value for both. I only want to get within the group, have both NULL and value.

Not sure what database system you are using, but if it support INTERSECT then you can use the following, if not you need to do something similar.

select * from table
where parentid in (
select parentid from table
where value is null
intersect
select parentid from table
where value is NOT null)