sql - Postgres：获取与组中其他列的最大值对应的列的值

Question

我正在尝试编写一个 postgres 查询，它返回组中的最大值、最小值、中值、第一个和最后一个值以及每个聚合值的时间戳列

桌子

Id Timestamp_utc                  Value
1  2020-11-05 15:36:15.768388     10
1  2020-11-05 15:40:15.768388     20
1  2020-11-05 15:44:15.768388     30
1  2020-11-05 15:45:15.768388.    5
1  2020-11-05 15:59:15.768388     25
1  2020-11-05 16:59:15.768388     25

预期结果

Id Median Median_Timestamp Min Min_Timestamp               Max Max_TimeStamp
1  17.5.  15:44:15.768388  5   2020-11-05 15:45:15.768388  30   2020-11-05 15:44:15.768388

我有这个查询哪些组数据不包括时间戳

SELECT Id, time_bucket('60', timestamp_utc) AS bucket,
percentile_cont(0.5) within group (order by value) median_value,
min(value) min_value, 
max(value) max_value 
FROM rs.MyTable 
WHERE id IN ( 1111,123)
AND timestamp_utc Between '2020-11-05 10:00:15.748643' and '2020-11-05 16:35:48.750313'
GROUP BY id, bucket 
ORDER BY id, bucket

当值为最大值时，有没有一种方法可以获取时间戳列以及诸如 timestamp_utc col 数据之类的聚合值？

标签： sqlpostgresqldatetimegreatest-n-per-grouptimescaledb

Answer 1

一种选择是在子查询中使用窗口函数通过递增和递减对时间戳进行排序value，然后在外部查询中进行条件聚合以获取相关值

select id, bucket,
    percentile_cont(0.5) within group (order by value) median_value,
    min(value) min_value, 
    max(timestamp_utc) filter(where rn_asc = 1) min_timestamp,
    max(value) max_value,
    max(timestamp_utc) filter(where rn_desc = 1) max_timestamp
from (
    select t.*, 
        row_number() over(partition by id, bucket order by value) rn_asc,
        row_number() over(partition by id, bucket order by value desc) rn_desc
    from (
        select t.*, time_bucket('60', timestamp_utc) as bucket 
        from rs.mytable t
        where 
            id in (1111,123)
            and timestamp_utc between '2020-11-05 10:00:15.748643'::timestamp 
                                  and '2020-11-05 16:35:48.750313'::timestamp
    ) t
) t
group by id, bucket 
order by id, bucket

注意，我们需要先计算bucket，然后放到window function的partition中。