Selecting values used by all identifiers

I have a SQL table which contains UserID and AppID. Now i need a select query which selects all appid’s which are used by all userid’s

For example:

UserID         AppID
1              35
1              42
2              35
2              42
3              35
3              77

In this example I would only want AppID 35 because it’s used by all UserID’s.

Answer

You can do aggregation :

select appid
from table t
group by appid
having count(*) = (select count(distinct userid) from table);

Use distinct inside count() in case appid has duplicate userid.