I have found this:
SELECT c.*
FROM contacts c
WHERE c.id IN ( SELECT p.contact_id FROM phone p WHERE p.addr = ? )
OR c.id IN (SELECT e.contact_id FROM email e WHERE e.addr = ? );
To have a worse plan than:
SELECT * FROM contacts where id IN (
( SELECT c.id FROM contacts c
JOIN phone p ON c.id = p.contact_id AND p.addr = ?
UNION
SELECT c.id FROM contacts c
JOIN email e ON c.id = e.contact_id AND e.addr = ? );
Maybe this is no surprise. But after discovering this my question is this, is there another option I dont' know about that is logically the same that can perform even better than the UNION?
