试试
where c.a1 not in (select a.a1 from a,b where a.a1=b.a1)
where b.a1 not in (select a.a1 from a,c where a.a1=c.a1)
from a where (a1 not in (select a1 from b)) and (a1 not in (select a1 from c))
where c.a1 not in (select a.a1 from a,b where a.a1=b.a1)
where b.a1 not in (select a.a1 from a,c where a.a1=c.a1)
from a where (a1 not in (select a1 from b)) and (a1 not in (select a1 from c))
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