聚合查询并显示非聚合列的最大值

Question

你好吗？我有这个问题：是否可以在 #col1 上使用 GroupBy 聚合查询，然后显示具有最高日期的 #col2 的值？

这个问题我遇到过很多次，我总是通过在我的代码中使用一些逻辑来解决这个问题，但如果可能的话，我很高兴知道。

举个实际例子：这个查询非常简单：它获取给定人员的所有薪水元素

SELECT dipElem.CodDip,
   dipElem.CodElemRetributivo as salElem,
   FORMAT(dipElem.DataInizioValidita, 'yyyy-MM-dd') AS datainizio,
   CONVERT(DECIMAL(10, 2), dipElem.ElemRetributivo) AS importo 
FROM JBADipendElemRetrib dipElem
     INNER JOIN JBAElemRetr elemRetr ON elemRetr.CodElemRetributivo = 
dipElem.CodElemRetributivo
WHERE dipElem.CodDitta = :CodDitta
    AND elemRetr.CodContratto = :CodContratto
    AND dipElem.CodDipendente = :CodDipendente
    AND dipElem.DBGruppo = 'GG'
ORDER BY dipElem.CodDipendente,
    dipElem.CodElemRetributivo ASC,
    dipElem.DataInizioValidita ASC;

而return是这样的：

CodDip	salElem	datainizio	importo
9	1	2019-11-04	989.18
9	1	2020-01-01	989.18
9	1	2020-11-01	1201.14
9	1	2021-11-01	1314.19
9	2	2019-11-04	0.00
9	5	2019-11-04	0.00
9	6	2019-11-04	0.00

但是，我想要 return 类似的东西：按 salElem 分组，其中 importo 最高 datainizio 可能 salElem.

CodDip	salElem	datainizio	importo
9	1	2021-11-01	1314.19
9	2	2019-11-04	0.00
9	5	2019-11-04	0.00
9	6	2019-11-04	0.00

Answer 1

这是一个通用的 greatest-n-per-group 查询。在 MySQL 8 或更高版本中，您可以使用 row_number window 函数：

with cte as (
    select t.*, row_number() over (partition by salElem order by datainizio desc) as rn
    from t
)
select *
from t
where rn = 1

Answer 2

为了结束这个问题并遵循 Salman A 的回答，这里是解决问题的代码（基于我的问题）：

WITH tmpTable AS (
    SELECT dipElem.CodElemRetributivo,
    FORMAT(dipElem.DataInizioValidita, 'yyyy-MM-dd') AS datainizio,
    CONVERT(DECIMAL(10, 2), dipElem.ElemRetributivo) AS importo,
    ROW_NUMBER() OVER (PARTITION BY dipElem.CodElemRetributivo
    ORDER BY dipElem.DataInizioValidita DESC)    AS my_rank
    FROM JBADipendElemRetrib dipElem
         INNER JOIN JBAElemRetr elemRetr ON elemRetr.CodElemRetributivo = dipElem.CodElemRetributivo
    WHERE dipElem.CodDitta = :CodDitta
        AND elemRetr.CodContratto = :CodContratto
        AND dipElem.CodDipendente = :CodDipendente
        AND dipElem.DBGruppo = 'GG'
)
SELECT *
FROM tmpTable
WHERE my_rank = 1;

聚合查询并显示非聚合列的最大值

Aggregate Query and display highest value of non-aggregated columns

mysql

sql

greatest-n-per-group