Question

This table lists events and users that are attending the event :

User         Event
 Joe            Movie
 Joe            Mall
 Jill              Mall
 Joe            Drinking
 Jenn          Drinking
 Jill              Drinking

How can I run a query on this table to list all the events that are common between 2 given users.

My guess is, this will need a self join, but I’m not sure.

Answer 1

SELECT *
FROM myTable joe
JOIN myTable jill ON jill.User='Jill' AND jill.Event=joe.Event
WHERE joe.User='Joe'

This might work also. It can sometimes be more efficient doing it this way (putting all conditions in the JOIN)

SELECT *
FROM myTable joe
JOIN myTable jill ON jill.User='Jill'
    AND jill.Event=joe.Event
    AND joe.User='Joe'