如何获取每组中的最大值和最小值以及它们的时间？

Question

假设我有一个 table MyTable，其中包含列 Id、NumericValue 和 UTCTimestamp。我正在尝试按时间戳的小时对 table MyTable 的结果进行分组，return 每个组的最大数值及其相关时间戳以及每个组的最小数值及其相关时间戳值。

现在，我可以通过以下查询解决问题的第一部分：

SELECT 
    HOUR(t.UTCTimestamp) AS `Hour`, 
    t.NumericValue AS MaximumValue,
    t.UTCTimestamp AS MaximumValueTime
FROM MyTable t
INNER JOIN (
    SELECT HOUR(t2.UTCTimestamp) AS `Hour`, MAX(t2.NumericValue) AS NumericValue
    FROM MyTable t2
    GROUP BY HOUR(t2.UTCTimestamp)
) maxNumericValue ON HOUR(t.UTCTimestamp) = maxNumericValue.`Hour` AND t.NumericValue = maxNumericValue.NumericValue
GROUP BY HOUR(t.UTCTimestamp);

其灵感来自 this answer。

Here's an MVCE.

如何显示每个组的最小值以及与之关联的时间戳？

Answer 1

应用相同的技术，但最少：

select a.*, b.MinimumValueTime from (
SELECT 
    HOUR(t.UTCTimestamp) AS `Hour`, 
    t.NumericValue AS MaximumValue,
    t.UTCTimestamp AS MaximumValueTime
FROM MyTable t
INNER JOIN (
    SELECT HOUR(t2.UTCTimestamp) AS `Hour`, MAX(t2.NumericValue) AS NumericValue
    FROM MyTable t2
    GROUP BY HOUR(t2.UTCTimestamp)
) maxNumericValue ON HOUR(t.UTCTimestamp) = maxNumericValue.`Hour` AND t.NumericValue = maxNumericValue.NumericValue
GROUP BY HOUR(t.UTCTimestamp))a
join
(
SELECT 
    HOUR(t.UTCTimestamp) AS `Hour`, 
    t.NumericValue AS MinimumValue,
    t.UTCTimestamp AS MinimumValueTime
FROM MyTable t
INNER JOIN (
    SELECT HOUR(t2.UTCTimestamp) AS `Hour`, MIN(t2.NumericValue) AS NumericValue
    FROM MyTable t2
    GROUP BY HOUR(t2.UTCTimestamp)
) minNumericValue ON HOUR(t.UTCTimestamp) = minNumericValue.`Hour` AND t.NumericValue = minNumericValue.NumericValue
GROUP BY HOUR(t.UTCTimestamp))b on a.hour=b.hour

Answer 2

从 MySQL 8.0 开始，您可以使用 ROW_NUMBER:

WITH cte AS (
  SELECT *,ROW_NUMBER() OVER(PARTITION BY HOUR(UTCTimestamp) 
                              ORDER BY UTCTimestamp ASC)  AS rn
          ,ROW_NUMBER() OVER(PARTITION BY HOUR(UTCTimestamp) 
                              ORDER BY UTCTimestamp DESC) AS rn2
  FROM MyTable
)
SELECT HOUR(c1.UTCTimestamp),
     c1.ID, c1.NumericValue, c1.UTCTimestamp,  -- min row
     c2.ID, c2.NumericValue, c2.UTCTimestamp   -- max row
FROM cte c1
JOIN cte c2
  ON HOUR(c1.UTCTimestamp) = HOUR(c2.UTCTimestamp)
  AND c1.rn=1
  AND c2.rn2=1
ORDER BY HOUR(c1.UTCTimestamp) ASC;

DBFiddle Demo

Answer 3

您可以加入 MyTable 两次（并且只能使用一个聚合子查询）

SELECT bounds.`Hour`
    , minT.NumericValue AS MinValue
    , minT.UTCTimestamp AS MinTime
    , maxT.NumericValue AS MaximumValue
    , maxT.UTCTimestamp AS MaximumValueTime
FROM (
    SELECT HOUR(t2.UTCTimestamp) AS `Hour`
         , MAX(t2.NumericValue) AS maxValue
         , MIN(t2.NumericValue) AS minValue
    FROM MyTable t2
    GROUP BY HOUR(t2.UTCTimestamp)
) bounds 
LEFT JOIN MyTable minT ON bounds.`Hour` = HOUR(minT.UTCTimestamp)
   AND bounds.minValue = minT.NumericValue
LEFT JOIN MyTable maxT ON bounds.`Hour` = HOUR(maxT.UTCTimestamp)
   AND bounds.maxValue = maxT.NumericValue
;

如何获取每组中的最大值和最小值以及它们的时间？

How to get the maximum and minimum values in each group as well as their times?

mysql

sql

greatest-n-per-group

mysql-5.6