Get unique values using STRING_AGG in SQL Server

Solution 1:

Use the DISTINCT keyword in a subquery to remove duplicates before combining the results: 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

Solution 2:

You can use distinct in the subquery used for the apply:

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;

Solution 3:

As @SeanLange pointed out in the comments, this is a terrible way to pull out the data, but if you had to, just make it 2 separate queries as follows:

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

That should do it.

Solution 4:

This is a function that I wrote that answers the OP Title: Improvements welcome!

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

Use like:

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