How to use GROUP BY to concatenate strings in SQL Server?

Question

How do I get:

id       Name       Value
1          A          4
1          B          8
2          C          9

to

id               


        

Answer 1

If you have clr enabled you could use the Group_Concat library from GitHub

Answer 2

I ran into a couple of problems when I tried converting Kevin Fairchild's suggestion to work with strings containing spaces and special XML characters (&, <, >) which were encoded.

The final version of my code (which doesn't answer the original question but may be useful to someone) looks like this:

CREATE TABLE #YourTable ([ID] INT, [Name] VARCHAR(MAX), [Value] INT)

INSERT INTO #YourTable ([ID],[Name],[Value]) VALUES (1,'Oranges & Lemons',4)
INSERT INTO #YourTable ([ID],[Name],[Value]) VALUES (1,'1 < 2',8)
INSERT INTO #YourTable ([ID],[Name],[Value]) VALUES (2,'C',9)

SELECT  [ID],
  STUFF((
    SELECT ', ' + CAST([Name] AS VARCHAR(MAX))
    FROM #YourTable WHERE (ID = Results.ID) 
    FOR XML PATH(''),TYPE 
     /* Use .value to uncomment XML entities e.g. &gt; &lt; etc*/
    ).value('.','VARCHAR(MAX)') 
  ,1,2,'') as NameValues
FROM    #YourTable Results
GROUP BY ID

DROP TABLE #YourTable

Rather than using a space as a delimiter and replacing all the spaces with commas, it just pre-pends a comma and space to each value then uses STUFF to remove the first two characters.

The XML encoding is taken care of automatically by using the TYPE directive.

Answer 3

SQL Server 2005 and later allow you to create your own custom aggregate functions, including for things like concatenation- see the sample at the bottom of the linked article.

Answer 4

Don't need a cursor... a while loop is sufficient.

------------------------------
-- Setup
------------------------------

DECLARE @Source TABLE
(
  id int,
  Name varchar(30),
  Value int
)

DECLARE @Target TABLE
(
  id int,
  Result varchar(max) 
)


INSERT INTO @Source(id, Name, Value) SELECT 1, 'A', 4
INSERT INTO @Source(id, Name, Value) SELECT 1, 'B', 8
INSERT INTO @Source(id, Name, Value) SELECT 2, 'C', 9


------------------------------
-- Technique
------------------------------

INSERT INTO @Target (id)
SELECT id
FROM @Source
GROUP BY id

DECLARE @id int, @Result varchar(max)
SET @id = (SELECT MIN(id) FROM @Target)

WHILE @id is not null
BEGIN
  SET @Result = null

  SELECT @Result =
    CASE
      WHEN @Result is null
      THEN ''
      ELSE @Result + ', '
    END + s.Name + ':' + convert(varchar(30),s.Value)
  FROM @Source s
  WHERE id = @id

  UPDATE @Target
  SET Result = @Result
  WHERE id = @id

  SET @id = (SELECT MIN(id) FROM @Target WHERE @id < id)
END

SELECT *
FROM @Target

Answer 5

Using Replace Function and FOR JSON PATH

SELECT T3.DEPT, REPLACE(REPLACE(T3.ENAME,'{"ENAME":"',''),'"}','') AS ENAME_LIST
FROM (
 SELECT DEPT, (SELECT ENAME AS [ENAME]
        FROM EMPLOYEE T2
        WHERE T2.DEPT=T1.DEPT
        FOR JSON PATH,WITHOUT_ARRAY_WRAPPER) ENAME
    FROM EMPLOYEE T1
    GROUP BY DEPT) T3

For sample data and more ways click here

Answer 6

This is just an addition to Kevin Fairchild's post (very clever by the way). I would have added it as a comment, but I don't have enough points yet :)

I was using this idea for a view I was working on, however the items I was concatinating contained spaces. So I modified the code slightly to not use spaces as delimiters.

Again thanks for the cool workaround Kevin!

CREATE TABLE #YourTable ( [ID] INT, [Name] CHAR(1), [Value] INT ) 

INSERT INTO #YourTable ([ID], [Name], [Value]) VALUES (1, 'A', 4) 
INSERT INTO #YourTable ([ID], [Name], [Value]) VALUES (1, 'B', 8) 
INSERT INTO #YourTable ([ID], [Name], [Value]) VALUES (2, 'C', 9) 

SELECT [ID], 
       REPLACE(REPLACE(REPLACE(
                          (SELECT [Name] + ':' + CAST([Value] AS VARCHAR(MAX)) as A 
                           FROM   #YourTable 
                           WHERE  ( ID = Results.ID ) 
                           FOR XML PATH (''))
                        , '</A><A>', ', ')
                ,'<A>','')
        ,'</A>','') AS NameValues 
FROM   #YourTable Results 
GROUP  BY ID 

DROP TABLE #YourTable