Oracle11g 获取具有相同密钥的不同记录数

假设我有一个表a：

我想获得具有相同B_ID的最大数量的不同记录，我还想知道B_ID在哪里发生。在这个例子中，我想得到值3和26

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实现这一点的最佳方法是什么？

最佳方法是简单的聚合+排序+限制返回的行数为1：

select b_id, no_of_records
from (
    select b_id, count(1) as no_of_records
    from table_A
    group by b_id
    order by no_of_records desc
)
where rownum <= 1;

当然，即使您有多个具有相同最高记录数的组，也会返回1行。如果您希望所有组具有相同的最高记录数，那么方法略有不同

select b_id, no_of_records
from (
    select b_id, count(1) as no_of_records,
        rank() over (partition by null order by count(1) desc) as rank$
    from table_A
    group by b_id
)
where rank$ <= 1;

select b_id, no_of_records
from (
    select b_id, count(1) as no_of_records,
        rank() over (partition by null order by count(1) desc) as rank$
    from table_A
    group by b_id
)
where rank$ <= 1;