Question

I have database structure as

User Table(user id, username, first name,last name)

Event Table(event id,event name, event date)

UserEvent(user id, event id)

I want to know username of all users who have participated in all events

Answer 1

That should do the trick

    SELECT u.id as user_id, u.username
FROM USER U,
(
        SELECT COUNT(EVENT_ID) AS EVENT_COUNT
        FROM EVENT
        ) AS E
    INNER JOIN (
        SELECT UDSER_ID, COUNT(EVENT_ID) AS EVENT_COUNT
        FROM USEREVENT
        GROUP BY USER_ID
        ) AS UE ON U.USER_ID = UE.USER_ID
WHERE E.EVENT_COUNT = UE.EVENT_COUNT