SQL Query to get aggregated result in comma separators along with group by column in SQL Server

I need to write a sql query on the table such that the result would have the group by column along with the aggregated column with comma separators.

My table would be in the below format

   |`````````|````````|
   |    ID   |  Value |
   |_________|________|
   |    1    |   a    |
   |_________|_____开发者_开发技巧___|
   |    1    |   b    |
   |_________|________|
   |    2    |   c    |
   |_________|________|

Expected result should be in the below format

   |`````````|````````|
   |    ID   |  Value |
   |_________|________|
   |    1    |  a,b   |
   |_________|________|
   |    2    |   c    |
   |_________|________|

---

You want to use FOR XML PATH construct:

select 
    ID, 
    stuff((select ', ' + Value 
           from YourTable t2 where t1.ID = t2.ID 
           for xml path('')),
          1,2,'') [Values]
from YourTable t1
group by ID

The STUFF function is to get rid of the leading ', '.

You can also see another examples here:

• SQL same unit between two tables needs order numbers in 1 cell
• SQL and Coldfusion left join tables getting duplicate results as a list in one column

---

Just for a balanced view, you can also do this with a CTE but its not as good as the cross apply method I don't think. I've coded this of the hoof so apologies if it doesn't work.

WITH CommaDelimitedCTE (RowNumber,ID,[Value],[Values]) AS
(
  SELECT 1,MT.ID , MIN(MT.Value), CAST(MIN(MT.Value) AS VARCHAR(8000)) 
  FROM  MyTable MT
  GROUP BY MT.ID

  UNION ALL

  SELECT CT.RowNumber + 1, MT.ID, MT.Value, CT.[Values] + ', ' + MT.Value
  FROM  MyTable MT
  INNER JOIN CommaDelimitedCTE CT ON CT.ID = MT.ID
  WHERE MT.[Value] > CT.[Value]
)

Select CommaDelimitedCTE.* from CommaDelimitedCTE 
    INNER JOIN (SELECT MT.ID,MAX(RowNumber) as MaxRowNumber from CommaDelimitedCTE GROUP BY MT.ID) Q on Q.MT.ID = CommaDelimitedCTE.MT.ID
    AND Q.MaxRowNumber = CommaDelimitedCTE.RowNumber

---

In SQL Server 2017 (14.x) and later you can use the STRING_AGG function:

https://learn.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql?view=sql-server-ver16

SELECT
  ID,
  STRING_AGG(Value, ',')
FROM TableName
GROUP BY ID

Depending on the data type of Value you might need to convert it:

SELECT
  ID,
  STRING_AGG(CONVERT(NVARCHAR(max), Value), ',')
FROM TableName
GROUP BY ID