i am facing a little problem in an sql query, 

here is the query

```
SELECT events.event_id,
( SELECT favorite_events.event_id, 
        (CASE favorite_events.event_id WHEN NULL THEN 0 ELSE 1 END)
        FROM favorite_events 
        WHERE favorite_events.event_id = events.event_id 
) AS is_favorite
FROM events 
WHERE start_date = 2013-07-16

```

it is giving me "Operand should contain 1 column(s)
" error, please help!