Deduplicate SELECT statements in relational division

I have a query that does a lot of duplicate work: SELECT visitor_id, '1'::text AS filter FROM events WHERE id IN (SELECT event_id FROM params WHERE key = 'utm_campaign' AND value = 'campaign_one') AND id IN (SELECT event_id FROM params WHERE key = 'utm_source' AND value = 'facebook') GROUP BY visitor_id UNION ALL SELECT visitor_id, '2'::text AS filter FROM events WHERE id IN (SELECT event_id FROM params WHERE key = 'utm_campaign' AND value = 'campaign_two') AND id IN (SELECT event_id FROM params WHERE key = 'utm_source' AND value = 'facebook') GROUP BY visitor_id As you can see, it performs different filtering on the params table 4 times. I'm using Redshift and although it scans this table very quickly, I have quite a few of these statements UNIONed together. Is there a way to rewrite the SQL using CASE/IF statements? The example uses key = 'utm_source' AND value = 'facebook' in both, but this is not necessarily true for all selects.