Question: How many categories in total do the app users who were not active when event no.2 happened belong to?
SQL: SELECT COUNT(*) FROM ( SELECT COUNT(DISTINCT T1.category) AS result FROM label_categories AS T1 INNER JOIN app_labels AS T2 ON T1.label_id = T2.label_id INNER JOIN app_events AS T3 ON T2.app_id = T3.app_id WHERE T3.event_id = 2 AND T3.is_active = 0 GROUP BY T1.category ) T