Sql 合并两列，然后按分组

我有下面的表格和数据，我想将loc1和loc2合并到一列中，并从loc列中删除重复值，然后根据group_no列对其进行分组

drop table test;
create table test (loc1 number(9), loc2 number(9), group_no number(9));
insert into test values(2,3,1);
insert into test values(2,9,1);
insert into test values(4,3,1);
insert into test values(6,8,2);
insert into test values(11,7,2);
insert into test values(20,15,2);
insert into test values(15,14,2);
insert into test values(21,31,3);
insert into test values(31,32,3);

预期结果如下：

loc   group_no
2        1
3        1
9        1
4        1
6        2
8        2 
11       2
20      2 
15       2
21       3
31       3
32       3

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根据您的预期结果，您希望按

loc

分组，而不是

group\u no

select t.loc, max(t.group_no)
(
    select loc1 as loc, group_no from test

    union

    select loc2 as loc, group_no from test
) t
group by t.loc
order by 2,1

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您能显示预期的结果吗？但分组方式不是按升序排列的