1.select id, class_name, class_name
from a, b, c
where a.class1=b.class_no
and a.class2=b.class_no上面语句1可能有问题,可以使用2
2.
select t1.id, t1.class_name, t2.class_name
from
(select id, class_name
from a, b
where a.class1 = b.class_NO) t1,
(select id, class_name
from a, c
where a.class2 = b.class_NO) t2
where t1.id = t2.id
from a, b, c
where a.class1=b.class_no
and a.class2=b.class_no上面语句1可能有问题,可以使用2
2.
select t1.id, t1.class_name, t2.class_name
from
(select id, class_name
from a, b
where a.class1 = b.class_NO) t1,
(select id, class_name
from a, c
where a.class2 = b.class_NO) t2
where t1.id = t2.id
where a.class1=x.class_no and
a.class2=y.class_no;