在 SQL Server 中使用 STRING_AGG 获取唯一值

Question

以下查询返回如下所示的结果：

SELECT 
    ProjectID, newID.value
FROM 
    [dbo].[Data] WITH(NOLOCK)  
CROSS APPLY 
    STRING_SPLIT([bID],';') AS newID  
WHERE 
    newID.value IN ('O95833', 'Q96NY7-2') 

结果：

ProjectID   value
---------------------
2           Q96NY7-2
2           O95833
2           O95833
2           Q96NY7-2
2           O95833
2           Q96NY7-2
4           Q96NY7-2
4           Q96NY7-2

使用新添加的STRING_AGG 函数（在 SQL Server 2017 中），如以下查询所示，我能够得到下面的结果集。

SELECT 
    ProjectID,
    STRING_AGG( newID.value, ',') WITHIN GROUP (ORDER BY newID.value) AS 
NewField
FROM
    [dbo].[Data] WITH(NOLOCK)  
CROSS APPLY 
    STRING_SPLIT([bID],';') AS newID  
WHERE 
    newID.value IN ('O95833', 'Q96NY7-2')  
GROUP BY 
    ProjectID
ORDER BY 
    ProjectID

结果：

ProjectID   NewField
-------------------------------------------------------------
2           O95833,O95833,O95833,Q96NY7-2,Q96NY7-2,Q96NY7-2
4           Q96NY7-2,Q96NY7-2

我希望我的最终输出只有如下独特的元素：

ProjectID   NewField
-------------------------------
2           O95833, Q96NY7-2
4           Q96NY7-2

关于如何获得此结果的任何建议？如果需要，请随时从头开始完善/重新设计我的查询。

Answer 1

Oracle（自版本 19c）suportslistagg (DISTINCT ...，但 Microsoft SQL Server 不太可能。

Answer 2

这是我编写的用于回答 OP 标题的函数： 欢迎改进！

CREATE OR ALTER FUNCTION [dbo].[fn_DistinctWords]
(
  @String NVARCHAR(MAX)  
)
RETURNS NVARCHAR(MAX)
WITH SCHEMABINDING
AS
BEGIN
  DECLARE @Result NVARCHAR(MAX);
  WITH MY_CTE AS ( SELECT Distinct(value) FROM STRING_SPLIT(@String, ' ')  )
  SELECT @Result = STRING_AGG(value, ' ') FROM MY_CTE
  RETURN @Result
END
GO

像这样使用：

SELECT dbo.fn_DistinctWords('One Two      Three Two One');

Answer 3

从STRING_AGG 获取唯一字符串的另一种可能性是在获取逗号分隔的字符串后执行这三个步骤：

1. 拆分字符串 (STRING_SPLIT)
2. 从拆分中选择DISTINCT
3. 再次将STRING_AGG 应用于单个键上的组选择

例子：

(select STRING_AGG(CAST(value as VARCHAR(MAX)), ',') 
        from (SELECT distinct 1 single_key, value 
            FROM STRING_SPLIT(STRING_AGG(CAST(customer_division as VARCHAR(MAX)), ','), ',')) 
                q group by single_key) as customer_division

Answer 4

您可以创建一个独特的表格视图，其中包含聚合值，这更加简单：

Create Table Test (field1 varchar(1), field2 varchar(1));

go

Create View DistinctTest as (Select distinct field1, field2 from test group by field1,field2);

go

insert into Test Select 'A', '1';
insert into Test Select 'A', '2';
insert into Test Select 'A', '2';
insert into Test Select 'A', '2';
insert into Test Select 'D', '1';
insert into Test Select 'D', '1';

select string_agg(field1, ',')  from Test where field2 = '1';  /* duplicates: A,D,D */;

select string_agg(field1, ',')  from DistinctTest where field2 = '1';  /* no duplicates: A,D  */;

Answer 5

正如@SeanLange 在 cmets 中指出的那样，这是一种提取数据的糟糕方法，但如果您不得不这样做，只需按如下方式进行 2 个单独的查询：

SELECT 
    ProjectID
    ,STRING_AGG( val, ',') WITHIN GROUP (ORDER BY val) AS NewField
FROM
(
    SELECT DISTINCT 
        ProjectID
        ,newID.value AS val
    FROM 
        [dbo].[Data] WITH(NOLOCK)  
        CROSS APPLY STRING_SPLIT([bID],';') AS newID  
    WHERE 
        newID.value IN ('O95833' , 'Q96NY7-2') 
) t
GROUP BY
    ProjectID

应该可以的。

Answer 6

您可以在用于apply 的子查询中使用distinct：

SELECT d.ProjectID,
       STRING_AGG(  newID.value, ',') WITHIN GROUP (ORDER BY newID.value) AS 
NewField
FROM [dbo].[Data] d CROSS APPLY
     (select distinct value
      from STRING_SPLIT(d.[bID], ';') AS newID 
     ) newID
WHERE newID.value IN (   'O95833' , 'Q96NY7-2'  ) 
group by projectid;

Answer 7

在合并结果之前在子查询中使用DISTINCT 关键字删除重复项：SQL Fiddle

SELECT 
ProjectID
,STRING_AGG(value, ',') WITHIN GROUP (ORDER BY value) AS 
NewField
from (
    select distinct ProjectId, newId.value 
    FROM [dbo].[Data] WITH(NOLOCK)  
    CROSS APPLY STRING_SPLIT([bID],';') AS newID  
    WHERE newID.value IN (   'O95833' , 'Q96NY7-2'  )  
) x
GROUP BY ProjectID
ORDER BY ProjectID