EXACTEMENT, MAIS T'AS OUBLIE UN DETAIL:
DECLARE @RequiredDeptID integer;
SET @RequiredDeptID=3; SELECT Events.[event_id], Events.[event_name]
FROM [dbo].[EVENT] AS Events
WHERE Events.[event_id] NOT IN (SELECT DISTINCT [event_id]
FROM [dbo].[ACTION] AS Actions
WHERE Actions.[dept_id] <> @RequiredDeptID
and Actions.[event_id]=event.[event_id] )
ouais man