Concat groups in SQL Server [duplicate] - sql

Question

This question already has answers here:
How to use GROUP BY to concatenate strings in SQL Server?
(22 answers)
Closed 8 years ago.
If I have a table like this:
+------------+
| Id | Value |
+------------+
| 1 | 'A' |
|------------|
| 1 | 'B' |
|------------|
| 2 | 'C' |
+------------+
How can I get a resultset like this:
+------------+
| Id | Value |
+------------+
| 1 | 'AB' |
|------------|
| 2 | 'C' |
+------------+
I know this is really easy to do in MySQL using GROUP_CONCAT, but I need to be able to do it in MSSQL 2005
Thanks
(Duplicate of How to use GROUP BY to concatenate strings in SQL Server?)

Answer 1

For a clean and efficient solution you can create an user defined aggregate function, there is even an example that does just what you need.
You can then use it like any other aggregate function (with a standard query plan):

Answer 2

This will do:
SELECT mt.ID,
SUBSTRING((SELECT mt2.Value
FROM MyTable AS mt2
WHERE mt2.ID = mt.ID
ORDER BY mt2.VALUE
FOR XML PATH('')), 3, 2000) AS JoinedValue
FROM MyTable AS mt

Answer 3

See:
http://blog.shlomoid.com/2008/11/emulating-mysqls-groupconcat-function.html

Answer 4

Often asked here.
The most efficient way is using the FOR XML PATH trick.

Answer 5

This just came to me as one possible solution. I have no idea as to performance, but I thought it would be an interesting way to solve the problem. I tested that it works in a simple situation (I didn't code to account for NULLs). Feel free to give it a test to see if it performs well for you.
The table that I used included an id (my_id). That could really be any column that is unique within the group (grp_id), so it could be a date column or whatever.
;WITH CTE AS (
SELECT
T1.my_id,
T1.grp_id,
CAST(T1.my_str AS VARCHAR) AS my_str
FROM
dbo.Test_Group_Concat T1
WHERE NOT EXISTS (SELECT * FROM dbo.Test_Group_Concat T2 WHERE T2.grp_id = T1.grp_id AND T2.my_id < T1.my_id)
UNION ALL
SELECT
T3.my_id,
T3.grp_id,
CAST(CTE.my_str + T3.my_str AS VARCHAR)
FROM
CTE
INNER JOIN dbo.Test_Group_Concat T3 ON
T3.grp_id = CTE.grp_id AND
T3.my_id > CTE.my_id
WHERE
NOT EXISTS (SELECT * FROM dbo.Test_Group_Concat T4 WHERE
T4.grp_id = CTE.grp_id AND
T4.my_id > CTE.my_id AND
T4.my_id < T3.my_id)
)
SELECT
CTE.grp_id,
CTE.my_str
FROM
CTE
INNER JOIN (SELECT grp_id, MAX(my_id) AS my_id FROM CTE GROUP BY grp_id) SQ ON
SQ.grp_id = CTE.grp_id AND
SQ.my_id = CTE.my_id
ORDER BY
CTE.grp_id