delete from occurrence_attribute_values where id in (
select oav.id
from occurrence_attribute_values oav
inner join occurrences o on o.id=oav.occurrence_id
inner join samples s on s.id=o.sample_id
where s.survey_id=7 
and s.created_on < '2010-04-22');

delete from sample_attribute_values where id in (
select sav.id
from sample_attribute_values sav
inner join samples s on s.id=sav.sample_id
where s.survey_id=7 
and s.created_on < '2010-04-22');

delete from occurrences
where sample_id in
 (select id from samples where survey_id=7 
and created_on < '2010-04-22');

delete from samples where survey_id=7 
and created_on < '2010-04-22';