Solution 2:
SELECT r.reg_id, r.date_registered, r.old_record, if(r.ghost_record!=0, (SELECT CONCAT(people.last_name, ', ', people.first_name) FROM people, registrants WHERE people.instance_id=12 and people.person_id=registrants.person_id AND registrants.reg_id=r.ghost_record), 'y') as registered_by_name
FROM registrants r
WHERE r.org_id=12
AND r.reg_status=0
AND r.reg_id=r.person_id
this way subquery will be executed "everytime", but I have everything on one place?
Because it has to evaluate the whole 'if' statement (including your subquery) for each row in the result set.
Best place to ask would be on the mysql mailing list:
http://lists.mysql.com/
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