SQL count of return users

Question

I'm trying to return a count of return users which happens when there is a duplicate 'user_id and action_type'.

So if you refer below, I would like my output to be = 2, since user_id (5) has 2 similar action_types (234) and user_id (6) also has 2 similar action_types (585).

How do I structure my query to reflect this?

Table t1
User_Id     Action_Type
---------   ------------
5           234
5           846
5           234
6           585
6           585 
7           465

Answer 1

SELECT COUNT(DISTINCT User_Id) FROM (
  SELECT   User_Id
  FROM     t1
  GROUP BY User_Id, Action_Type
  HAVING   COUNT(*) > 1
) t