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Equivalent MySQL group_concat in SQL Server

Posted on 2015-02-22
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Last Modified: 2015-02-23
Hi,
My table looks like this:
Field1      Field2
1              A
1              B
1              C
2              A
2              B
With this mysql command select field1, group_concat(field2) as field2 from t1 Group by field1, I could achieve this:
Field1   Field2
1            A,B,C
2            A,B
How can I achieve this SQL Server 2008 R2
Regards
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Question by:Omer-Pitou
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2 Comments
 
LVL 18

Expert Comment

by:Simon
ID: 40624537
It can be done in MSSQL with a little more effort, using a recursive CTE (common table expression). The code below was originally written by Quassnoi and posted on his ExplainExtended.com blog
WITH
        qs(Field1,Field2, rn, cnt) AS
        (
        SELECT  Field1,Field2,
                ROW_NUMBER() OVER (PARTITION BY Field1 ORDER BY Field2),
                COUNT(*) OVER (PARTITION BY Field1)
        FROM    Table1
        ),
        t (Field1,Field2, gc, rn, cnt) AS
        (
        SELECT  Field1,Field2,
                CAST(Field2 AS NVARCHAR(MAX)), rn, cnt
        FROM    qs
        WHERE   rn = 1
        UNION ALL
        SELECT  qs.Field1, qs.Field2,
                CAST(t.gc + ', ' + qs.Field2 AS NVARCHAR(MAX)),
                qs.rn, qs.cnt
        FROM    t
        JOIN    qs
        ON      qs.Field1 = t.Field1
                AND qs.rn = t.rn + 1
        )
SELECT  Field1, gc as Field2
FROM    t
WHERE   rn = cnt
order by Field1
OPTION (MAXRECURSION 0)

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See it working here on SQL Fiddle
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LVL 48

Accepted Solution

by:
PortletPaul earned 500 total points
ID: 40625364
the T-SQL "FOR XML PATH" is the closest equivalent to group_concat() I believe

SELECT DISTINCT
      T1.Field1, CA.value
FROM Table1 T1
CROSS APPLY (
           SELECT
              STUFF(
                    (
                    SELECT
                          ', ' + T2.Field2
                    FROM Table1 AS T2
                    WHERE T2.Field1 = T1.Field1
                    ORDER BY T2.Field2
                    FOR XML PATH ('')
                    )
                   , 1, 1, '')
           ) ca (value)
;

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Lines 7 to 14 relate to FOR XML PATH
Lines 5, 6 & 15 related to STUFF() which is simply used here to remove the first comma in the concatenated string
Note the use of CROSS APPLY which allows correlated subqueries into the FROM clause

see a demo here: http://sqlfiddle.com/#!3/5358b/3 
execution plan:  http://sqlfiddle.com/#!3/5358b/3/0



details
**MS SQL Server 2008 Schema Setup**:

    
    CREATE TABLE Table1
    	([Field1] int, [Field2] varchar(1))
    ;
    	
    INSERT INTO Table1
    	([Field1], [Field2])
    VALUES
    	(1, 'A'),
    	(1, 'B'),
    	(1, 'C'),
    	(2, 'A'),
    	(2, 'B'),
        (3, 'Z'),
    	(3, 'Y'),
    	(3, 'T'),
        (3, 'S')
    ;

**Query 1**:

    SELECT DISTINCT
          T1.Field1, CA.value
    FROM Table1 T1
    CROSS APPLY (
               SELECT
                  STUFF(
                        (
                        SELECT
                              ', ' + T2.Field2
                        FROM Table1 AS T2
                        WHERE T2.Field1 = T1.Field1
                        ORDER BY T2.Field2
                        FOR XML PATH ('')
                        )
                       , 1, 1, '')
               ) ca (value)
    

**[Results][2]**:
    
    | FIELD1 |       VALUE |
    |--------|-------------|
    |      1 |     A, B, C |
    |      2 |        A, B |
    |      3 |  S, T, Y, Z |



  [1]: http://sqlfiddle.com/#!3/5358b/3

  [2]: http://sqlfiddle.com/#!3/5358b/3/0

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