这些条件可以使用 case 中的表达式 order by 函数如下 row_number .

select A,B,frequency,timekey
from (select t.*
            ,row_number() over(partition by A order by cast((B = 'unknown') as int), B) as rnum
      from tbl t
     ) t 
where rnum = 1

在这里，对于每一组行，我们对除 B = 'unknown' 先是，然后是 B 价值观。

使用 row_number 解析函数。如果要选择“不” unknown 先录制，然后使用以下查询：

select  A, B, Frequency, timekey
from
(select 
       A, B, Frequency, timekey,
       row_number() over(partition by A,Frequency order by case when B='unknown' then 1 else 0 end) rn
)s where rn=1

如果你想选择 unknown 如果它们存在，就用这个 row_number 在上面的查询中：

row_number() over(partition by A,Frequency order by case when B='unknown' then 0 else 1 end) rn