Oracle SQL为一组分组结果中的每个组获取具有MAX值的行[重复]答案

【问题标题】：Oracle SQL get row with MAX value for each group in a set of grouped results [duplicate]Oracle SQL为一组分组结果中的每个组获取具有MAX值的行[重复]
【发布时间】：2019-07-30 14:49:17
【问题描述】：

我有一组通过运行得到的结果

SELECT 
       REV_USAGE_DATA.DDATE, 
       REV_USAGE_DATA.SEGMENT, 
       COUNT(*) AS Freq
FROM CADA_PERMSISDN_DASH REV_USAGE_DATA
GROUP BY 
       REV_USAGE_DATA.DDATE,
       REV_USAGE_DATA.SEGMENT
ORDER BY 
REV_USAGE_DATA.DDATE

对于每个日期，我想获取 FREQ 列中具有最高值的整行。我怎样才能做到这一点？

【问题讨论】：

标签： sql oracle greatest-n-per-group

【解决方案1】：

您可以使用 CTE

WITH CTE0 AS 
(
  SELECT 
       REV_USAGE_DATA.DDATE, 
       REV_USAGE_DATA.SEGMENT, 
       COUNT(*) AS Freq
  FROM CADA_PERMSISDN_DASH REV_USAGE_DATA
  GROUP BY 
       REV_USAGE_DATA.DDATE,
       REV_USAGE_DATA.SEGMENT
)
SELECT 
  DDATE,
  SEGMENT, 
  FREQ
FROM CTE0 
WHERE (DDATE, SEGMENT, FREQ) IN (
  SELECT DDATE, MAX(SEGMENT), MAX(FREQ)
  FROM CTE0 
  GROUP BY DDATE
)

【讨论】：

就像一个魅力。谢谢

【解决方案2】：

使用ROW_NUMBER():

SELECT DDATE, SEGMENT, Freq
FROM (SELECT REV_USAGE_DATA.DDATE, REV_USAGE_DATA.SEGMENT, 
             COUNT(*) AS Freq,
             ROW_NUMBER() OVER (PARTITION BY REV_USAGE_DATA.DDATE ORDER BY COUNT(*) DESC) as seqnum
      FROM CADA_PERMSISDN_DASH REV_USAGE_DATA
      GROUP BY REV_USAGE_DATA.DDATE,REV_USAGE_DATA.SEGMENT
     ) rud
WHERE seqnum = 1
ORDER BY REV_USAGE_DATA.DDATE;

如果您在某个日期打成平手，并且想要所有最高值，请改用 RANK()。

【讨论】：

谢谢，但是这给了我每个日期 4 行。事实上，它重现了我在问题中分享的相同结果集。
@tendaitakas。 . .对。它会这样做不是吗？我添加了执行您想要的过滤的 where 子句。

【解决方案3】：

很多类似的解决方案！这是我的。使用 CTE 计算频率最高的记录（类似于 row-number）然后选择它们

WITH data AS
(
  SELECT 
       REV_USAGE_DATA.DDATE, 
       REV_USAGE_DATA.SEGMENT, 
       COUNT(*) AS Freq
  FROM CADA_PERMSISDN_DASH REV_USAGE_DATA
  GROUP BY 
         REV_USAGE_DATA.DDATE,
         REV_USAGE_DATA.SEGMENT
),
maxRecords AS
(
  SELECT DDATE, SEGMENT, FREQ, 
         CASE WHEN FREQ = MAX(FREQ) OVER(PARTITION BY DDATE) THEN 1 ELSE 0 END HighestFreq
  FROM data
)

SELECT DDATE, SEGMENT, FREQ
FROM maxRecords
WHERE HighestFreq = 1
ORDER BY DDATE;

【讨论】：