如何获取最大值并使用group by子句

Question

我有这样的查询：

select transactions_id,
    time_stamp,
    clock
from times
group by transactions_id
having sum(distinct type) = 1

现在，我希望获得max值，具体取决于id。

我使用了以下查询但未使用过：

select max(id),
    transactions_id,
    time_stamp,
    clock
from times
group by transactions_id
having sum(distinct type) = 1

或

select transactions_id,
    time_stamp,
    clock
from times
group by transactions_id
having sum(distinct type) = 1
    and max(id)

例如：

我有三个条件：

1. type必须为1
2. group by transactions_id
3. max id

Answer 1

您可以在一个查询中找到聚合，并将其结果与表结合以获取相关行。

select *
from times t1
join (
    select transactions_id,
        max(id) as id
    from times
    where type = 1
    group by transactions_id
    ) t2 using (transactions_id, id);

Answer 2

如果我理解正确，您可以使用ANSI标准row_number()函数：

select t.*
from (select t.*,
             row_number() over (partition by transactions_id order by id desc) as seqnum
      from times t
     ) t
where seqnum = 1;

我不确定having sum(distinct type) = 1是什么。这个问题没有在问题中解释。