SQL：如何从 string_Agg() 函数中获取不同的值？

Question

以下代码

SELECT 
      DISTINCT(p.ID) AS ID
    , PIT.Code AS Code
    , year(PT.Date) AS Year
FROM fact.PreT PT
INNER JOIN dim.ProdIType PIT 
    ON PIT.ProdITypeSKey = PT.ProdITypeSKey
INNER JOIN dim.Proudct P
    ON P.ProductSKey = pt.ProductSKey
WHERE p.ID = '15'
GROUP BY p.ID, PIT.Code, PT.Year

返回以下内容：

我已经重新配置了我的脚本以添加聚合并按 id 和年份对代码进行分组，但是发现了重复项。 代码和输出如下：

SELECT 
      DISTINCT(p.ID) AS ID
    , string_agg(PIT.Code, ',') AS Code
    , year(PT.Date) AS Year
FROM fact.PreT PT
INNER JOIN dim.ProdIType PIT 
    ON PIT.ProdITypeSKey = PT.ProdITypeSKey
INNER JOIN dim.Proudct P
    ON P.ProductSKey = pt.ProductSKey
WHERE p.ID = '15'
GROUP BY p.ID, PT.Year

结果：

所需的输出 - 不同且有序的代码升序：

有人可以解释为什么 string_acc 是重复代码吗？ 我应该如何解决这个问题？

Answer 1

您需要对其进行子查询并再次分组。 请注意， DISTINCT不是函数，它作用于整个结果集，并且与按所有列分组相同。

SELECT 
      ID
    , string_agg(Code, ',') AS Code
    , [Year]
FROM (
    SELECT
          p.ID
        , PIT.Code AS Code
        , year(PT.Date) AS Year
    FROM fact.PreT PT
    INNER JOIN dim.ProdIType PIT 
        ON PIT.ProdITypeSKey = PT.ProdITypeSKey
    INNER JOIN dim.Proudct P
        ON P.ProductSKey = pt.ProductSKey
    WHERE p.ID = '15'
    GROUP BY p.ID, year(PT.Date), PIT.Code
) p
GROUP BY p.ID, PT.Year;