Re: select problem

(SELECT * from mydata,city WHERE mydata.sample = 1 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))
INTERSECT
(SELECT * from mydata,city WHERE mydata.sample = 2 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))

EXCEPT
(
(SELECT * from mydata,city WHERE mydata.sample = 2 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))
INTERSECT
(SELECT * from mydata,city WHERE mydata.sample = 3 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))
)

UNION

(SELECT * from mydata,city WHERE mydata.sample = 1 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))
INTERSECT
(SELECT * from mydata,city WHERE mydata.sample = 3 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))

EXCEPT
(
(SELECT * from mydata,city WHERE mydata.sample = 2 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))
INTERSECT
(SELECT * from mydata,city WHERE mydata.sample = 3 AND
mydata.age_from >= city.age_from AND mydata.age_to <= city.age_to AND
basen not in ('A', 'T', 'G','C'))
)

ps:
Here is set 1, 2, 3.
our target: (set 1 INTERSECT set 2) EXCEPT (set 2 INTERSECT set 3) UNION (set 1 INTERSECT set 3) EXCEPT (set 2 INTERSECT set 3).
your data is not correct.