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Well, you might try this approach:
First, find all of the distinct visitor_id values that did attend on a given date.
select distinct visitor_id from attendance
where date = '2004-10-12'
Then select what you want from the VISITOR table where the visitor_id is not in the first list.
select distinct .... from visitor
where visitor_id not in (select distinct visitor_id from attendance
where date = '2004-10-12')
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